v0.17.0 (October 9, 2015)

This is a major release from 0.16.2 and includes a small number of API changes, several new features, enhancements, and performance improvements along with a large number of bug fixes. We recommend that all users upgrade to this version.

Warning

pandas >= 0.17.0 will no longer support compatibility with Python version 3.2 (GH9118)

Warning

The pandas.io.data package is deprecated and will be replaced by the pandas-datareader package. This will allow the data modules to be independently updated to your pandas installation. The API for pandas-datareader v0.1.1 is exactly the same as in pandas v0.17.0 (GH8961, GH10861).

After installing pandas-datareader, you can easily change your imports:

from pandas.io import data, wb

becomes

from pandas_datareader import data, wb

Highlights include:

  • Release the Global Interpreter Lock (GIL) on some cython operations, see here
  • Plotting methods are now available as attributes of the .plot accessor, see here
  • The sorting API has been revamped to remove some long-time inconsistencies, see here
  • Support for a datetime64[ns] with timezones as a first-class dtype, see here
  • The default for to_datetime will now be to raise when presented with unparseable formats, previously this would return the original input. Also, date parse functions now return consistent results. See here
  • The default for dropna in HDFStore has changed to False, to store by default all rows even if they are all NaN, see here
  • Datetime accessor (dt) now supports Series.dt.strftime to generate formatted strings for datetime-likes, and Series.dt.total_seconds to generate each duration of the timedelta in seconds. See here
  • Period and PeriodIndex can handle multiplied freq like 3D, which corresponding to 3 days span. See here
  • Development installed versions of pandas will now have PEP440 compliant version strings (GH9518)
  • Development support for benchmarking with the Air Speed Velocity library (GH8361)
  • Support for reading SAS xport files, see here
  • Documentation comparing SAS to pandas, see here
  • Removal of the automatic TimeSeries broadcasting, deprecated since 0.8.0, see here
  • Display format with plain text can optionally align with Unicode East Asian Width, see here
  • Compatibility with Python 3.5 (GH11097)
  • Compatibility with matplotlib 1.5.0 (GH11111)

Check the API Changes and deprecations before updating.

New features

Datetime with TZ

We are adding an implementation that natively supports datetime with timezones. A Series or a DataFrame column previously could be assigned a datetime with timezones, and would work as an object dtype. This had performance issues with a large number rows. See the docs for more details. (GH8260, GH10763, GH11034).

The new implementation allows for having a single-timezone across all rows, with operations in a performant manner.

In [1]: df = DataFrame({'A' : date_range('20130101',periods=3),
   ...:                 'B' : date_range('20130101',periods=3,tz='US/Eastern'),
   ...:                 'C' : date_range('20130101',periods=3,tz='CET')})
   ...: 

In [2]: df
Out[2]: 
           A                         B                         C
0 2013-01-01 2013-01-01 00:00:00-05:00 2013-01-01 00:00:00+01:00
1 2013-01-02 2013-01-02 00:00:00-05:00 2013-01-02 00:00:00+01:00
2 2013-01-03 2013-01-03 00:00:00-05:00 2013-01-03 00:00:00+01:00

[3 rows x 3 columns]

In [3]: df.dtypes
Out[3]: 
A                datetime64[ns]
B    datetime64[ns, US/Eastern]
C           datetime64[ns, CET]
Length: 3, dtype: object
In [4]: df.B
Out[4]: 
0   2013-01-01 00:00:00-05:00
1   2013-01-02 00:00:00-05:00
2   2013-01-03 00:00:00-05:00
Name: B, Length: 3, dtype: datetime64[ns, US/Eastern]

In [5]: df.B.dt.tz_localize(None)
Out[5]: 
0   2013-01-01
1   2013-01-02
2   2013-01-03
Name: B, Length: 3, dtype: datetime64[ns]

This uses a new-dtype representation as well, that is very similar in look-and-feel to its numpy cousin datetime64[ns]

In [6]: df['B'].dtype
Out[6]: datetime64[ns, US/Eastern]

In [7]: type(df['B'].dtype)
Out[7]: pandas.core.dtypes.dtypes.DatetimeTZDtype

Note

There is a slightly different string repr for the underlying DatetimeIndex as a result of the dtype changes, but functionally these are the same.

Previous Behavior:

In [1]: pd.date_range('20130101',periods=3,tz='US/Eastern')
Out[1]: DatetimeIndex(['2013-01-01 00:00:00-05:00', '2013-01-02 00:00:00-05:00',
                       '2013-01-03 00:00:00-05:00'],
                      dtype='datetime64[ns]', freq='D', tz='US/Eastern')

In [2]: pd.date_range('20130101',periods=3,tz='US/Eastern').dtype
Out[2]: dtype('<M8[ns]')

New Behavior:

In [8]: pd.date_range('20130101',periods=3,tz='US/Eastern')
Out[8]: 
DatetimeIndex(['2013-01-01 00:00:00-05:00', '2013-01-02 00:00:00-05:00',
               '2013-01-03 00:00:00-05:00'],
              dtype='datetime64[ns, US/Eastern]', freq='D')

In [9]: pd.date_range('20130101',periods=3,tz='US/Eastern').dtype
Out[9]: datetime64[ns, US/Eastern]

Releasing the GIL

We are releasing the global-interpreter-lock (GIL) on some cython operations. This will allow other threads to run simultaneously during computation, potentially allowing performance improvements from multi-threading. Notably groupby, nsmallest, value_counts and some indexing operations benefit from this. (GH8882)

For example the groupby expression in the following code will have the GIL released during the factorization step, e.g. df.groupby('key') as well as the .sum() operation.

N = 1000000
ngroups = 10
df = DataFrame({'key' : np.random.randint(0,ngroups,size=N),
                'data' : np.random.randn(N) })
df.groupby('key')['data'].sum()

Releasing of the GIL could benefit an application that uses threads for user interactions (e.g. QT), or performing multi-threaded computations. A nice example of a library that can handle these types of computation-in-parallel is the dask library.

Plot submethods

The Series and DataFrame .plot() method allows for customizing plot types by supplying the kind keyword arguments. Unfortunately, many of these kinds of plots use different required and optional keyword arguments, which makes it difficult to discover what any given plot kind uses out of the dozens of possible arguments.

To alleviate this issue, we have added a new, optional plotting interface, which exposes each kind of plot as a method of the .plot attribute. Instead of writing series.plot(kind=<kind>, ...), you can now also use series.plot.<kind>(...):

In [10]: df = pd.DataFrame(np.random.rand(10, 2), columns=['a', 'b'])

In [11]: df.plot.bar()
../_images/whatsnew_plot_submethods.png

As a result of this change, these methods are now all discoverable via tab-completion:

In [12]: df.plot.<TAB>
df.plot.area     df.plot.barh     df.plot.density  df.plot.hist     df.plot.line     df.plot.scatter
df.plot.bar      df.plot.box      df.plot.hexbin   df.plot.kde      df.plot.pie

Each method signature only includes relevant arguments. Currently, these are limited to required arguments, but in the future these will include optional arguments, as well. For an overview, see the new Plotting API documentation.

Additional methods for dt accessor

strftime

We are now supporting a Series.dt.strftime method for datetime-likes to generate a formatted string (GH10110). Examples:

# DatetimeIndex
In [13]: s = pd.Series(pd.date_range('20130101', periods=4))

In [14]: s
Out[14]: 
0   2013-01-01
1   2013-01-02
2   2013-01-03
3   2013-01-04
Length: 4, dtype: datetime64[ns]

In [15]: s.dt.strftime('%Y/%m/%d')
Out[15]: 
0    2013/01/01
1    2013/01/02
2    2013/01/03
3    2013/01/04
Length: 4, dtype: object
# PeriodIndex
In [16]: s = pd.Series(pd.period_range('20130101', periods=4))

In [17]: s
Out[17]: 
0    2013-01-01
1    2013-01-02
2    2013-01-03
3    2013-01-04
Length: 4, dtype: period[D]

In [18]: s.dt.strftime('%Y/%m/%d')
Out[18]: 
0    2013/01/01
1    2013/01/02
2    2013/01/03
3    2013/01/04
Length: 4, dtype: object

The string format is as the python standard library and details can be found here

total_seconds

pd.Series of type timedelta64 has new method .dt.total_seconds() returning the duration of the timedelta in seconds (GH10817)

# TimedeltaIndex
In [19]: s = pd.Series(pd.timedelta_range('1 minutes', periods=4))

In [20]: s
Out[20]: 
0   0 days 00:01:00
1   1 days 00:01:00
2   2 days 00:01:00
3   3 days 00:01:00
Length: 4, dtype: timedelta64[ns]

In [21]: s.dt.total_seconds()
Out[21]: 
0        60.0
1     86460.0
2    172860.0
3    259260.0
Length: 4, dtype: float64

Period Frequency Enhancement

Period, PeriodIndex and period_range can now accept multiplied freq. Also, Period.freq and PeriodIndex.freq are now stored as a DateOffset instance like DatetimeIndex, and not as str (GH7811)

A multiplied freq represents a span of corresponding length. The example below creates a period of 3 days. Addition and subtraction will shift the period by its span.

In [22]: p = pd.Period('2015-08-01', freq='3D')

In [23]: p
Out[23]: Period('2015-08-01', '3D')

In [24]: p + 1
Out[24]: Period('2015-08-04', '3D')

In [25]: p - 2
Out[25]: Period('2015-07-26', '3D')

In [26]: p.to_timestamp()
Out[26]: Timestamp('2015-08-01 00:00:00')

In [27]: p.to_timestamp(how='E')
Out[27]: Timestamp('2015-08-03 23:59:59.999999999')

You can use the multiplied freq in PeriodIndex and period_range.

In [28]: idx = pd.period_range('2015-08-01', periods=4, freq='2D')

In [29]: idx
Out[29]: PeriodIndex(['2015-08-01', '2015-08-03', '2015-08-05', '2015-08-07'], dtype='period[2D]', freq='2D')

In [30]: idx + 1
Out[30]: PeriodIndex(['2015-08-03', '2015-08-05', '2015-08-07', '2015-08-09'], dtype='period[2D]', freq='2D')

Support for SAS XPORT files

read_sas() provides support for reading SAS XPORT format files. (GH4052).

df = pd.read_sas('sas_xport.xpt')

It is also possible to obtain an iterator and read an XPORT file incrementally.

for df in pd.read_sas('sas_xport.xpt', chunksize=10000)
    do_something(df)

See the docs for more details.

Support for Math Functions in .eval()

eval() now supports calling math functions (GH4893)

df = pd.DataFrame({'a': np.random.randn(10)})
df.eval("b = sin(a)")

The support math functions are sin, cos, exp, log, expm1, log1p, sqrt, sinh, cosh, tanh, arcsin, arccos, arctan, arccosh, arcsinh, arctanh, abs and arctan2.

These functions map to the intrinsics for the NumExpr engine. For the Python engine, they are mapped to NumPy calls.

Changes to Excel with MultiIndex

In version 0.16.2 a DataFrame with MultiIndex columns could not be written to Excel via to_excel. That functionality has been added (GH10564), along with updating read_excel so that the data can be read back with, no loss of information, by specifying which columns/rows make up the MultiIndex in the header and index_col parameters (GH4679)

See the documentation for more details.

In [31]: df = pd.DataFrame([[1,2,3,4], [5,6,7,8]],
   ....:                   columns = pd.MultiIndex.from_product([['foo','bar'],['a','b']],
   ....:                                                        names = ['col1', 'col2']),
   ....:                   index = pd.MultiIndex.from_product([['j'], ['l', 'k']],
   ....:                                                      names = ['i1', 'i2']))
   ....: 

In [32]: df
Out[32]: 
col1  foo    bar   
col2    a  b   a  b
i1 i2              
j  l    1  2   3  4
   k    5  6   7  8

[2 rows x 4 columns]

In [33]: df.to_excel('test.xlsx')

In [34]: df = pd.read_excel('test.xlsx', header=[0,1], index_col=[0,1])

In [35]: df
Out[35]: 
col1  foo    bar   
col2    a  b   a  b
i1 i2              
j  l    1  2   3  4
   k    5  6   7  8

[2 rows x 4 columns]

Previously, it was necessary to specify the has_index_names argument in read_excel, if the serialized data had index names. For version 0.17.0 the output format of to_excel has been changed to make this keyword unnecessary - the change is shown below.

Old

../_images/old-excel-index.png

New

../_images/new-excel-index.png

Warning

Excel files saved in version 0.16.2 or prior that had index names will still able to be read in, but the has_index_names argument must specified to True.

Google BigQuery Enhancements

  • Added ability to automatically create a table/dataset using the pandas.io.gbq.to_gbq() function if the destination table/dataset does not exist. (GH8325, GH11121).
  • Added ability to replace an existing table and schema when calling the pandas.io.gbq.to_gbq() function via the if_exists argument. See the docs for more details (GH8325).
  • InvalidColumnOrder and InvalidPageToken in the gbq module will raise ValueError instead of IOError.
  • The generate_bq_schema() function is now deprecated and will be removed in a future version (GH11121)
  • The gbq module will now support Python 3 (GH11094).

Display Alignment with Unicode East Asian Width

Warning

Enabling this option will affect the performance for printing of DataFrame and Series (about 2 times slower). Use only when it is actually required.

Some East Asian countries use Unicode characters its width is corresponding to 2 alphabets. If a DataFrame or Series contains these characters, the default output cannot be aligned properly. The following options are added to enable precise handling for these characters.

  • display.unicode.east_asian_width: Whether to use the Unicode East Asian Width to calculate the display text width. (GH2612)
  • display.unicode.ambiguous_as_wide: Whether to handle Unicode characters belong to Ambiguous as Wide. (GH11102)
In [36]: df = pd.DataFrame({u'国籍': ['UK', u'日本'], u'名前': ['Alice', u'しのぶ']})

In [37]: df;
../_images/option_unicode011.png
In [38]: pd.set_option('display.unicode.east_asian_width', True)

In [39]: df;
../_images/option_unicode021.png

For further details, see here

Other enhancements

  • Support for openpyxl >= 2.2. The API for style support is now stable (GH10125)

  • merge now accepts the argument indicator which adds a Categorical-type column (by default called _merge) to the output object that takes on the values (GH8790)

    Observation Origin _merge value
    Merge key only in 'left' frame left_only
    Merge key only in 'right' frame right_only
    Merge key in both frames both
    In [40]: df1 = pd.DataFrame({'col1':[0,1], 'col_left':['a','b']})
    
    In [41]: df2 = pd.DataFrame({'col1':[1,2,2],'col_right':[2,2,2]})
    
    In [42]: pd.merge(df1, df2, on='col1', how='outer', indicator=True)
    Out[42]: 
       col1 col_left  col_right      _merge
    0     0        a        NaN   left_only
    1     1        b        2.0        both
    2     2      NaN        2.0  right_only
    3     2      NaN        2.0  right_only
    
    [4 rows x 4 columns]
    

    For more, see the updated docs

  • pd.to_numeric is a new function to coerce strings to numbers (possibly with coercion) (GH11133)

  • pd.merge will now allow duplicate column names if they are not merged upon (GH10639).

  • pd.pivot will now allow passing index as None (GH3962).

  • pd.concat will now use existing Series names if provided (GH10698).

    In [43]: foo = pd.Series([1,2], name='foo')
    
    In [44]: bar = pd.Series([1,2])
    
    In [45]: baz = pd.Series([4,5])
    

    Previous Behavior:

    In [1] pd.concat([foo, bar, baz], 1)
    Out[1]:
          0  1  2
       0  1  1  4
       1  2  2  5
    

    New Behavior:

    In [46]: pd.concat([foo, bar, baz], 1)
    Out[46]: 
       foo  0  1
    0    1  1  4
    1    2  2  5
    
    [2 rows x 3 columns]
    
  • DataFrame has gained the nlargest and nsmallest methods (GH10393)

  • Add a limit_direction keyword argument that works with limit to enable interpolate to fill NaN values forward, backward, or both (GH9218, GH10420, GH11115)

    In [47]: ser = pd.Series([np.nan, np.nan, 5, np.nan, np.nan, np.nan, 13])
    
    In [48]: ser.interpolate(limit=1, limit_direction='both')
    Out[48]: 
    0     NaN
    1     5.0
    2     5.0
    3     7.0
    4     NaN
    5    11.0
    6    13.0
    Length: 7, dtype: float64
    
  • Added a DataFrame.round method to round the values to a variable number of decimal places (GH10568).

    In [49]: df = pd.DataFrame(np.random.random([3, 3]), columns=['A', 'B', 'C'],
       ....: index=['first', 'second', 'third'])
       ....: 
    
    In [50]: df
    Out[50]: 
                   A         B         C
    first   0.126970  0.966718  0.260476
    second  0.897237  0.376750  0.336222
    third   0.451376  0.840255  0.123102
    
    [3 rows x 3 columns]
    
    In [51]: df.round(2)
    Out[51]: 
               A     B     C
    first   0.13  0.97  0.26
    second  0.90  0.38  0.34
    third   0.45  0.84  0.12
    
    [3 rows x 3 columns]
    
    In [52]: df.round({'A': 0, 'C': 2})
    Out[52]: 
              A         B     C
    first   0.0  0.966718  0.26
    second  1.0  0.376750  0.34
    third   0.0  0.840255  0.12
    
    [3 rows x 3 columns]
    
  • drop_duplicates and duplicated now accept a keep keyword to target first, last, and all duplicates. The take_last keyword is deprecated, see here (GH6511, GH8505)

    In [53]: s = pd.Series(['A', 'B', 'C', 'A', 'B', 'D'])
    
    In [54]: s.drop_duplicates()
    Out[54]: 
    0    A
    1    B
    2    C
    5    D
    Length: 4, dtype: object
    
    In [55]: s.drop_duplicates(keep='last')
    Out[55]: 
    2    C
    3    A
    4    B
    5    D
    Length: 4, dtype: object
    
    In [56]: s.drop_duplicates(keep=False)
    Out[56]: 
    2    C
    5    D
    Length: 2, dtype: object
    
  • Reindex now has a tolerance argument that allows for finer control of Limits on filling while reindexing (GH10411):

    In [57]: df = pd.DataFrame({'x': range(5),
       ....:                    't': pd.date_range('2000-01-01', periods=5)})
       ....: 
    
    In [58]: df.reindex([0.1, 1.9, 3.5],
       ....:            method='nearest',
       ....:            tolerance=0.2)
       ....: 
    Out[58]: 
           x          t
    0.1  0.0 2000-01-01
    1.9  2.0 2000-01-03
    3.5  NaN        NaT
    
    [3 rows x 2 columns]
    

    When used on a DatetimeIndex, TimedeltaIndex or PeriodIndex, tolerance will coerced into a Timedelta if possible. This allows you to specify tolerance with a string:

    In [59]: df = df.set_index('t')
    
    In [60]: df.reindex(pd.to_datetime(['1999-12-31']),
       ....:            method='nearest',
       ....:            tolerance='1 day')
       ....: 
    Out[60]: 
                x
    1999-12-31  0
    
    [1 rows x 1 columns]
    

    tolerance is also exposed by the lower level Index.get_indexer and Index.get_loc methods.

  • Added functionality to use the base argument when resampling a TimeDeltaIndex (GH10530)

  • DatetimeIndex can be instantiated using strings contains NaT (GH7599)

  • to_datetime can now accept the yearfirst keyword (GH7599)

  • pandas.tseries.offsets larger than the Day offset can now be used with a Series for addition/subtraction (GH10699). See the docs for more details.

  • pd.Timedelta.total_seconds() now returns Timedelta duration to ns precision (previously microsecond precision) (GH10939)

  • PeriodIndex now supports arithmetic with np.ndarray (GH10638)

  • Support pickling of Period objects (GH10439)

  • .as_blocks will now take a copy optional argument to return a copy of the data, default is to copy (no change in behavior from prior versions), (GH9607)

  • regex argument to DataFrame.filter now handles numeric column names instead of raising ValueError (GH10384).

  • Enable reading gzip compressed files via URL, either by explicitly setting the compression parameter or by inferring from the presence of the HTTP Content-Encoding header in the response (GH8685)

  • Enable writing Excel files in memory using StringIO/BytesIO (GH7074)

  • Enable serialization of lists and dicts to strings in ExcelWriter (GH8188)

  • SQL io functions now accept a SQLAlchemy connectable. (GH7877)

  • pd.read_sql and to_sql can accept database URI as con parameter (GH10214)

  • read_sql_table will now allow reading from views (GH10750).

  • Enable writing complex values to HDFStores when using the table format (GH10447)

  • Enable pd.read_hdf to be used without specifying a key when the HDF file contains a single dataset (GH10443)

  • pd.read_stata will now read Stata 118 type files. (GH9882)

  • msgpack submodule has been updated to 0.4.6 with backward compatibility (GH10581)

  • DataFrame.to_dict now accepts orient='index' keyword argument (GH10844).

  • DataFrame.apply will return a Series of dicts if the passed function returns a dict and reduce=True (GH8735).

  • Allow passing kwargs to the interpolation methods (GH10378).

  • Improved error message when concatenating an empty iterable of Dataframe objects (GH9157)

  • pd.read_csv can now read bz2-compressed files incrementally, and the C parser can read bz2-compressed files from AWS S3 (GH11070, GH11072).

  • In pd.read_csv, recognize s3n:// and s3a:// URLs as designating S3 file storage (GH11070, GH11071).

  • Read CSV files from AWS S3 incrementally, instead of first downloading the entire file. (Full file download still required for compressed files in Python 2.) (GH11070, GH11073)

  • pd.read_csv is now able to infer compression type for files read from AWS S3 storage (GH11070, GH11074).

Backwards incompatible API changes

Changes to sorting API

The sorting API has had some longtime inconsistencies. (GH9816, GH8239).

Here is a summary of the API PRIOR to 0.17.0:

  • Series.sort is INPLACE while DataFrame.sort returns a new object.
  • Series.order returns a new object
  • It was possible to use Series/DataFrame.sort_index to sort by values by passing the by keyword.
  • Series/DataFrame.sortlevel worked only on a MultiIndex for sorting by index.

To address these issues, we have revamped the API:

  • We have introduced a new method, DataFrame.sort_values(), which is the merger of DataFrame.sort(), Series.sort(), and Series.order(), to handle sorting of values.
  • The existing methods Series.sort(), Series.order(), and DataFrame.sort() have been deprecated and will be removed in a future version.
  • The by argument of DataFrame.sort_index() has been deprecated and will be removed in a future version.
  • The existing method .sort_index() will gain the level keyword to enable level sorting.

We now have two distinct and non-overlapping methods of sorting. A * marks items that will show a FutureWarning.

To sort by the values:

Previous Replacement
* Series.order() Series.sort_values()
* Series.sort() Series.sort_values(inplace=True)
* DataFrame.sort(columns=...) DataFrame.sort_values(by=...)

To sort by the index:

Previous Replacement
Series.sort_index() Series.sort_index()
Series.sortlevel(level=...) Series.sort_index(level=...)
DataFrame.sort_index() DataFrame.sort_index()
DataFrame.sortlevel(level=...) DataFrame.sort_index(level=...)
* DataFrame.sort() DataFrame.sort_index()

We have also deprecated and changed similar methods in two Series-like classes, Index and Categorical.

Previous Replacement
* Index.order() Index.sort_values()
* Categorical.order() Categorical.sort_values()

Changes to to_datetime and to_timedelta

Error handling

The default for pd.to_datetime error handling has changed to errors='raise'. In prior versions it was errors='ignore'. Furthermore, the coerce argument has been deprecated in favor of errors='coerce'. This means that invalid parsing will raise rather that return the original input as in previous versions. (GH10636)

Previous Behavior:

In [2]: pd.to_datetime(['2009-07-31', 'asd'])
Out[2]: array(['2009-07-31', 'asd'], dtype=object)

New Behavior:

In [3]: pd.to_datetime(['2009-07-31', 'asd'])
ValueError: Unknown string format

Of course you can coerce this as well.

In [61]: to_datetime(['2009-07-31', 'asd'], errors='coerce')
Out[61]: DatetimeIndex(['2009-07-31', 'NaT'], dtype='datetime64[ns]', freq=None)

To keep the previous behavior, you can use errors='ignore':

In [62]: to_datetime(['2009-07-31', 'asd'], errors='ignore')
Out[62]: Index(['2009-07-31', 'asd'], dtype='object')

Furthermore, pd.to_timedelta has gained a similar API, of errors='raise'|'ignore'|'coerce', and the coerce keyword has been deprecated in favor of errors='coerce'.

Consistent Parsing

The string parsing of to_datetime, Timestamp and DatetimeIndex has been made consistent. (GH7599)

Prior to v0.17.0, Timestamp and to_datetime may parse year-only datetime-string incorrectly using today’s date, otherwise DatetimeIndex uses the beginning of the year. Timestamp and to_datetime may raise ValueError in some types of datetime-string which DatetimeIndex can parse, such as a quarterly string.

Previous Behavior:

In [1]: Timestamp('2012Q2')
Traceback
   ...
ValueError: Unable to parse 2012Q2

# Results in today's date.
In [2]: Timestamp('2014')
Out [2]: 2014-08-12 00:00:00

v0.17.0 can parse them as below. It works on DatetimeIndex also.

New Behavior:

In [63]: Timestamp('2012Q2')
Out[63]: Timestamp('2012-04-01 00:00:00')

In [64]: Timestamp('2014')
Out[64]: Timestamp('2014-01-01 00:00:00')

In [65]: DatetimeIndex(['2012Q2', '2014'])
Out[65]: DatetimeIndex(['2012-04-01', '2014-01-01'], dtype='datetime64[ns]', freq=None)

Note

If you want to perform calculations based on today’s date, use Timestamp.now() and pandas.tseries.offsets.

In [66]: import pandas.tseries.offsets as offsets

In [67]: Timestamp.now()
Out[67]: Timestamp('2018-12-11 06:00:57.888746')

In [68]: Timestamp.now() + offsets.DateOffset(years=1)
Out[68]: Timestamp('2019-12-11 06:00:57.889947')

Changes to Index Comparisons

Operator equal on Index should behavior similarly to Series (GH9947, GH10637)

Starting in v0.17.0, comparing Index objects of different lengths will raise a ValueError. This is to be consistent with the behavior of Series.

Previous Behavior:

In [2]: pd.Index([1, 2, 3]) == pd.Index([1, 4, 5])
Out[2]: array([ True, False, False], dtype=bool)

In [3]: pd.Index([1, 2, 3]) == pd.Index([2])
Out[3]: array([False,  True, False], dtype=bool)

In [4]: pd.Index([1, 2, 3]) == pd.Index([1, 2])
Out[4]: False

New Behavior:

In [8]: pd.Index([1, 2, 3]) == pd.Index([1, 4, 5])
Out[8]: array([ True, False, False], dtype=bool)

In [9]: pd.Index([1, 2, 3]) == pd.Index([2])
ValueError: Lengths must match to compare

In [10]: pd.Index([1, 2, 3]) == pd.Index([1, 2])
ValueError: Lengths must match to compare

Note that this is different from the numpy behavior where a comparison can be broadcast:

In [69]: np.array([1, 2, 3]) == np.array([1])
Out[69]: array([ True, False, False], dtype=bool)

or it can return False if broadcasting can not be done:

In [70]: np.array([1, 2, 3]) == np.array([1, 2])
Out[70]: False

Changes to Boolean Comparisons vs. None

Boolean comparisons of a Series vs None will now be equivalent to comparing with np.nan, rather than raise TypeError. (GH1079).

In [71]: s = Series(range(3))

In [72]: s.iloc[1] = None

In [73]: s
Out[73]: 
0    0.0
1    NaN
2    2.0
Length: 3, dtype: float64

Previous Behavior:

In [5]: s==None
TypeError: Could not compare <type 'NoneType'> type with Series

New Behavior:

In [74]: s==None
Out[74]: 
0    False
1    False
2    False
Length: 3, dtype: bool

Usually you simply want to know which values are null.

In [75]: s.isnull()
Out[75]: 
0    False
1     True
2    False
Length: 3, dtype: bool

Warning

You generally will want to use isnull/notnull for these types of comparisons, as isnull/notnull tells you which elements are null. One has to be mindful that nan's don’t compare equal, but None's do. Note that Pandas/numpy uses the fact that np.nan != np.nan, and treats None like np.nan.

In [76]: None == None
Out[76]: True

In [77]: np.nan == np.nan
Out[77]: False

HDFStore dropna behavior

The default behavior for HDFStore write functions with format='table' is now to keep rows that are all missing. Previously, the behavior was to drop rows that were all missing save the index. The previous behavior can be replicated using the dropna=True option. (GH9382)

Previous Behavior:

In [78]: df_with_missing = pd.DataFrame({'col1':[0, np.nan, 2],
   ....:                                 'col2':[1, np.nan, np.nan]})
   ....: 

In [79]: df_with_missing
Out[79]: 
   col1  col2
0   0.0   1.0
1   NaN   NaN
2   2.0   NaN

[3 rows x 2 columns]
In [27]:
df_with_missing.to_hdf('file.h5',
                       'df_with_missing',
                       format='table',
                       mode='w')

In [28]: pd.read_hdf('file.h5', 'df_with_missing')

Out [28]:
      col1  col2
  0     0     1
  2     2   NaN

New Behavior:

In [80]: df_with_missing.to_hdf('file.h5',
   ....:                        'df_with_missing',
   ....:                         format='table',
   ....:                         mode='w')
   ....: 

In [81]: pd.read_hdf('file.h5', 'df_with_missing')
Out[81]: 
   col1  col2
0   0.0   1.0
1   NaN   NaN
2   2.0   NaN

[3 rows x 2 columns]

See the docs for more details.

Changes to display.precision option

The display.precision option has been clarified to refer to decimal places (GH10451).

Earlier versions of pandas would format floating point numbers to have one less decimal place than the value in display.precision.

In [1]: pd.set_option('display.precision', 2)

In [2]: pd.DataFrame({'x': [123.456789]})
Out[2]:
       x
0  123.5

If interpreting precision as “significant figures” this did work for scientific notation but that same interpretation did not work for values with standard formatting. It was also out of step with how numpy handles formatting.

Going forward the value of display.precision will directly control the number of places after the decimal, for regular formatting as well as scientific notation, similar to how numpy’s precision print option works.

In [82]: pd.set_option('display.precision', 2)

In [83]: pd.DataFrame({'x': [123.456789]})
Out[83]: 
        x
0  123.46

[1 rows x 1 columns]

To preserve output behavior with prior versions the default value of display.precision has been reduced to 6 from 7.

Changes to Categorical.unique

Categorical.unique now returns new Categoricals with categories and codes that are unique, rather than returning np.array (GH10508)

  • unordered category: values and categories are sorted by appearance order.
  • ordered category: values are sorted by appearance order, categories keep existing order.
In [84]: cat = pd.Categorical(['C', 'A', 'B', 'C'],
   ....:                      categories=['A', 'B', 'C'],
   ....:                      ordered=True)
   ....: 

In [85]: cat
Out[85]: 
[C, A, B, C]
Categories (3, object): [A < B < C]

In [86]: cat.unique()
Out[86]: 
[C, A, B]
Categories (3, object): [A < B < C]

In [87]: cat = pd.Categorical(['C', 'A', 'B', 'C'],
   ....:                      categories=['A', 'B', 'C'])
   ....: 

In [88]: cat
Out[88]: 
[C, A, B, C]
Categories (3, object): [A, B, C]

In [89]: cat.unique()
Out[89]: 
[C, A, B]
Categories (3, object): [C, A, B]

Changes to bool passed as header in Parsers

In earlier versions of pandas, if a bool was passed the header argument of read_csv, read_excel, or read_html it was implicitly converted to an integer, resulting in header=0 for False and header=1 for True (GH6113)

A bool input to header will now raise a TypeError

In [29]: df = pd.read_csv('data.csv', header=False)
TypeError: Passing a bool to header is invalid. Use header=None for no header or
header=int or list-like of ints to specify the row(s) making up the column names

Other API Changes

  • Line and kde plot with subplots=True now uses default colors, not all black. Specify color='k' to draw all lines in black (GH9894)

  • Calling the .value_counts() method on a Series with a categorical dtype now returns a Series with a CategoricalIndex (GH10704)

  • The metadata properties of subclasses of pandas objects will now be serialized (GH10553).

  • groupby using Categorical follows the same rule as Categorical.unique described above (GH10508)

  • When constructing DataFrame with an array of complex64 dtype previously meant the corresponding column was automatically promoted to the complex128 dtype. Pandas will now preserve the itemsize of the input for complex data (GH10952)

  • some numeric reduction operators would return ValueError, rather than TypeError on object types that includes strings and numbers (GH11131)

  • Passing currently unsupported chunksize argument to read_excel or ExcelFile.parse will now raise NotImplementedError (GH8011)

  • Allow an ExcelFile object to be passed into read_excel (GH11198)

  • DatetimeIndex.union does not infer freq if self and the input have None as freq (GH11086)

  • NaT’s methods now either raise ValueError, or return np.nan or NaT (GH9513)

    Behavior Methods
    return np.nan weekday, isoweekday
    return NaT date, now, replace, to_datetime, today
    return np.datetime64('NaT') to_datetime64 (unchanged)
    raise ValueError All other public methods (names not beginning with underscores)

Deprecations

  • For Series the following indexing functions are deprecated (GH10177).

    Deprecated Function Replacement
    .irow(i) .iloc[i] or .iat[i]
    .iget(i) .iloc[i] or .iat[i]
    .iget_value(i) .iloc[i] or .iat[i]
  • For DataFrame the following indexing functions are deprecated (GH10177).

    Deprecated Function Replacement
    .irow(i) .iloc[i]
    .iget_value(i, j) .iloc[i, j] or .iat[i, j]
    .icol(j) .iloc[:, j]

Note

These indexing function have been deprecated in the documentation since 0.11.0.

  • Categorical.name was deprecated to make Categorical more numpy.ndarray like. Use Series(cat, name="whatever") instead (GH10482).
  • Setting missing values (NaN) in a Categorical’s categories will issue a warning (GH10748). You can still have missing values in the values.
  • drop_duplicates and duplicated’s take_last keyword was deprecated in favor of keep. (GH6511, GH8505)
  • Series.nsmallest and nlargest’s take_last keyword was deprecated in favor of keep. (GH10792)
  • DataFrame.combineAdd and DataFrame.combineMult are deprecated. They can easily be replaced by using the add and mul methods: DataFrame.add(other, fill_value=0) and DataFrame.mul(other, fill_value=1.) (GH10735).
  • TimeSeries deprecated in favor of Series (note that this has been an alias since 0.13.0), (GH10890)
  • SparsePanel deprecated and will be removed in a future version (GH11157).
  • Series.is_time_series deprecated in favor of Series.index.is_all_dates (GH11135)
  • Legacy offsets (like 'A@JAN') are deprecated (note that this has been alias since 0.8.0) (GH10878)
  • WidePanel deprecated in favor of Panel, LongPanel in favor of DataFrame (note these have been aliases since < 0.11.0), (GH10892)
  • DataFrame.convert_objects has been deprecated in favor of type-specific functions pd.to_datetime, pd.to_timestamp and pd.to_numeric (new in 0.17.0) (GH11133).

Removal of prior version deprecations/changes

  • Removal of na_last parameters from Series.order() and Series.sort(), in favor of na_position. (GH5231)

  • Remove of percentile_width from .describe(), in favor of percentiles. (GH7088)

  • Removal of colSpace parameter from DataFrame.to_string(), in favor of col_space, circa 0.8.0 version.

  • Removal of automatic time-series broadcasting (GH2304)

    In [90]: np.random.seed(1234)
    
    In [91]: df = DataFrame(np.random.randn(5,2),columns=list('AB'),index=date_range('20130101',periods=5))
    
    In [92]: df
    Out[92]: 
                       A         B
    2013-01-01  0.471435 -1.190976
    2013-01-02  1.432707 -0.312652
    2013-01-03 -0.720589  0.887163
    2013-01-04  0.859588 -0.636524
    2013-01-05  0.015696 -2.242685
    
    [5 rows x 2 columns]
    

    Previously

    In [3]: df + df.A
    FutureWarning: TimeSeries broadcasting along DataFrame index by default is deprecated.
    Please use DataFrame.<op> to explicitly broadcast arithmetic operations along the index
    
    Out[3]:
                        A         B
    2013-01-01  0.942870 -0.719541
    2013-01-02  2.865414  1.120055
    2013-01-03 -1.441177  0.166574
    2013-01-04  1.719177  0.223065
    2013-01-05  0.031393 -2.226989
    

    Current

    In [93]: df.add(df.A,axis='index')
    Out[93]: 
                       A         B
    2013-01-01  0.942870 -0.719541
    2013-01-02  2.865414  1.120055
    2013-01-03 -1.441177  0.166574
    2013-01-04  1.719177  0.223065
    2013-01-05  0.031393 -2.226989
    
    [5 rows x 2 columns]
    
  • Remove table keyword in HDFStore.put/append, in favor of using format= (GH4645)

  • Remove kind in read_excel/ExcelFile as its unused (GH4712)

  • Remove infer_type keyword from pd.read_html as its unused (GH4770, GH7032)

  • Remove offset and timeRule keywords from Series.tshift/shift, in favor of freq (GH4853, GH4864)

  • Remove pd.load/pd.save aliases in favor of pd.to_pickle/pd.read_pickle (GH3787)

Performance Improvements

  • Development support for benchmarking with the Air Speed Velocity library (GH8361)
  • Added vbench benchmarks for alternative ExcelWriter engines and reading Excel files (GH7171)
  • Performance improvements in Categorical.value_counts (GH10804)
  • Performance improvements in SeriesGroupBy.nunique and SeriesGroupBy.value_counts and SeriesGroupby.transform (GH10820, GH11077)
  • Performance improvements in DataFrame.drop_duplicates with integer dtypes (GH10917)
  • Performance improvements in DataFrame.duplicated with wide frames. (GH10161, GH11180)
  • 4x improvement in timedelta string parsing (GH6755, GH10426)
  • 8x improvement in timedelta64 and datetime64 ops (GH6755)
  • Significantly improved performance of indexing MultiIndex with slicers (GH10287)
  • 8x improvement in iloc using list-like input (GH10791)
  • Improved performance of Series.isin for datetimelike/integer Series (GH10287)
  • 20x improvement in concat of Categoricals when categories are identical (GH10587)
  • Improved performance of to_datetime when specified format string is ISO8601 (GH10178)
  • 2x improvement of Series.value_counts for float dtype (GH10821)
  • Enable infer_datetime_format in to_datetime when date components do not have 0 padding (GH11142)
  • Regression from 0.16.1 in constructing DataFrame from nested dictionary (GH11084)
  • Performance improvements in addition/subtraction operations for DateOffset with Series or DatetimeIndex (GH10744, GH11205)

Bug Fixes

  • Bug in incorrect computation of .mean() on timedelta64[ns] because of overflow (GH9442)
  • Bug in .isin on older numpies (GH11232)
  • Bug in DataFrame.to_html(index=False) renders unnecessary name row (GH10344)
  • Bug in DataFrame.to_latex() the column_format argument could not be passed (GH9402)
  • Bug in DatetimeIndex when localizing with NaT (GH10477)
  • Bug in Series.dt ops in preserving meta-data (GH10477)
  • Bug in preserving NaT when passed in an otherwise invalid to_datetime construction (GH10477)
  • Bug in DataFrame.apply when function returns categorical series. (GH9573)
  • Bug in to_datetime with invalid dates and formats supplied (GH10154)
  • Bug in Index.drop_duplicates dropping name(s) (GH10115)
  • Bug in Series.quantile dropping name (GH10881)
  • Bug in pd.Series when setting a value on an empty Series whose index has a frequency. (GH10193)
  • Bug in pd.Series.interpolate with invalid order keyword values. (GH10633)
  • Bug in DataFrame.plot raises ValueError when color name is specified by multiple characters (GH10387)
  • Bug in Index construction with a mixed list of tuples (GH10697)
  • Bug in DataFrame.reset_index when index contains NaT. (GH10388)
  • Bug in ExcelReader when worksheet is empty (GH6403)
  • Bug in BinGrouper.group_info where returned values are not compatible with base class (GH10914)
  • Bug in clearing the cache on DataFrame.pop and a subsequent inplace op (GH10912)
  • Bug in indexing with a mixed-integer Index causing an ImportError (GH10610)
  • Bug in Series.count when index has nulls (GH10946)
  • Bug in pickling of a non-regular freq DatetimeIndex (GH11002)
  • Bug causing DataFrame.where to not respect the axis parameter when the frame has a symmetric shape. (GH9736)
  • Bug in Table.select_column where name is not preserved (GH10392)
  • Bug in offsets.generate_range where start and end have finer precision than offset (GH9907)
  • Bug in pd.rolling_* where Series.name would be lost in the output (GH10565)
  • Bug in stack when index or columns are not unique. (GH10417)
  • Bug in setting a Panel when an axis has a MultiIndex (GH10360)
  • Bug in USFederalHolidayCalendar where USMemorialDay and USMartinLutherKingJr were incorrect (GH10278 and GH9760 )
  • Bug in .sample() where returned object, if set, gives unnecessary SettingWithCopyWarning (GH10738)
  • Bug in .sample() where weights passed as Series were not aligned along axis before being treated positionally, potentially causing problems if weight indices were not aligned with sampled object. (GH10738)
  • Regression fixed in (GH9311, GH6620, GH9345), where groupby with a datetime-like converting to float with certain aggregators (GH10979)
  • Bug in DataFrame.interpolate with axis=1 and inplace=True (GH10395)
  • Bug in io.sql.get_schema when specifying multiple columns as primary key (GH10385).
  • Bug in groupby(sort=False) with datetime-like Categorical raises ValueError (GH10505)
  • Bug in groupby(axis=1) with filter() throws IndexError (GH11041)
  • Bug in test_categorical on big-endian builds (GH10425)
  • Bug in Series.shift and DataFrame.shift not supporting categorical data (GH9416)
  • Bug in Series.map using categorical Series raises AttributeError (GH10324)
  • Bug in MultiIndex.get_level_values including Categorical raises AttributeError (GH10460)
  • Bug in pd.get_dummies with sparse=True not returning SparseDataFrame (GH10531)
  • Bug in Index subtypes (such as PeriodIndex) not returning their own type for .drop and .insert methods (GH10620)
  • Bug in algos.outer_join_indexer when right array is empty (GH10618)
  • Bug in filter (regression from 0.16.0) and transform when grouping on multiple keys, one of which is datetime-like (GH10114)
  • Bug in to_datetime and to_timedelta causing Index name to be lost (GH10875)
  • Bug in len(DataFrame.groupby) causing IndexError when there’s a column containing only NaNs (GH11016)
  • Bug that caused segfault when resampling an empty Series (GH10228)
  • Bug in DatetimeIndex and PeriodIndex.value_counts resets name from its result, but retains in result’s Index. (GH10150)
  • Bug in pd.eval using numexpr engine coerces 1 element numpy array to scalar (GH10546)
  • Bug in pd.concat with axis=0 when column is of dtype category (GH10177)
  • Bug in read_msgpack where input type is not always checked (GH10369, GH10630)
  • Bug in pd.read_csv with kwargs index_col=False, index_col=['a', 'b'] or dtype (GH10413, GH10467, GH10577)
  • Bug in Series.from_csv with header kwarg not setting the Series.name or the Series.index.name (GH10483)
  • Bug in groupby.var which caused variance to be inaccurate for small float values (GH10448)
  • Bug in Series.plot(kind='hist') Y Label not informative (GH10485)
  • Bug in read_csv when using a converter which generates a uint8 type (GH9266)
  • Bug causes memory leak in time-series line and area plot (GH9003)
  • Bug when setting a Panel sliced along the major or minor axes when the right-hand side is a DataFrame (GH11014)
  • Bug that returns None and does not raise NotImplementedError when operator functions (e.g. .add) of Panel are not implemented (GH7692)
  • Bug in line and kde plot cannot accept multiple colors when subplots=True (GH9894)
  • Bug in DataFrame.plot raises ValueError when color name is specified by multiple characters (GH10387)
  • Bug in left and right align of Series with MultiIndex may be inverted (GH10665)
  • Bug in left and right join of with MultiIndex may be inverted (GH10741)
  • Bug in read_stata when reading a file with a different order set in columns (GH10757)
  • Bug in Categorical may not representing properly when category contains tz or Period (GH10713)
  • Bug in Categorical.__iter__ may not returning correct datetime and Period (GH10713)
  • Bug in indexing with a PeriodIndex on an object with a PeriodIndex (GH4125)
  • Bug in read_csv with engine='c': EOF preceded by a comment, blank line, etc. was not handled correctly (GH10728, GH10548)
  • Reading “famafrench” data via DataReader results in HTTP 404 error because of the website url is changed (GH10591).
  • Bug in read_msgpack where DataFrame to decode has duplicate column names (GH9618)
  • Bug in io.common.get_filepath_or_buffer which caused reading of valid S3 files to fail if the bucket also contained keys for which the user does not have read permission (GH10604)
  • Bug in vectorised setting of timestamp columns with python datetime.date and numpy datetime64 (GH10408, GH10412)
  • Bug in Index.take may add unnecessary freq attribute (GH10791)
  • Bug in merge with empty DataFrame may raise IndexError (GH10824)
  • Bug in to_latex where unexpected keyword argument for some documented arguments (GH10888)
  • Bug in indexing of large DataFrame where IndexError is uncaught (GH10645 and GH10692)
  • Bug in read_csv when using the nrows or chunksize parameters if file contains only a header line (GH9535)
  • Bug in serialization of category types in HDF5 in presence of alternate encodings. (GH10366)
  • Bug in pd.DataFrame when constructing an empty DataFrame with a string dtype (GH9428)
  • Bug in pd.DataFrame.diff when DataFrame is not consolidated (GH10907)
  • Bug in pd.unique for arrays with the datetime64 or timedelta64 dtype that meant an array with object dtype was returned instead the original dtype (GH9431)
  • Bug in Timedelta raising error when slicing from 0s (GH10583)
  • Bug in DatetimeIndex.take and TimedeltaIndex.take may not raise IndexError against invalid index (GH10295)
  • Bug in Series([np.nan]).astype('M8[ms]'), which now returns Series([pd.NaT]) (GH10747)
  • Bug in PeriodIndex.order reset freq (GH10295)
  • Bug in date_range when freq divides end as nanos (GH10885)
  • Bug in iloc allowing memory outside bounds of a Series to be accessed with negative integers (GH10779)
  • Bug in read_msgpack where encoding is not respected (GH10581)
  • Bug preventing access to the first index when using iloc with a list containing the appropriate negative integer (GH10547, GH10779)
  • Bug in TimedeltaIndex formatter causing error while trying to save DataFrame with TimedeltaIndex using to_csv (GH10833)
  • Bug in DataFrame.where when handling Series slicing (GH10218, GH9558)
  • Bug where pd.read_gbq throws ValueError when Bigquery returns zero rows (GH10273)
  • Bug in to_json which was causing segmentation fault when serializing 0-rank ndarray (GH9576)
  • Bug in plotting functions may raise IndexError when plotted on GridSpec (GH10819)
  • Bug in plot result may show unnecessary minor ticklabels (GH10657)
  • Bug in groupby incorrect computation for aggregation on DataFrame with NaT (E.g first, last, min). (GH10590, GH11010)
  • Bug when constructing DataFrame where passing a dictionary with only scalar values and specifying columns did not raise an error (GH10856)
  • Bug in .var() causing roundoff errors for highly similar values (GH10242)
  • Bug in DataFrame.plot(subplots=True) with duplicated columns outputs incorrect result (GH10962)
  • Bug in Index arithmetic may result in incorrect class (GH10638)
  • Bug in date_range results in empty if freq is negative annually, quarterly and monthly (GH11018)
  • Bug in DatetimeIndex cannot infer negative freq (GH11018)
  • Remove use of some deprecated numpy comparison operations, mainly in tests. (GH10569)
  • Bug in Index dtype may not applied properly (GH11017)
  • Bug in io.gbq when testing for minimum google api client version (GH10652)
  • Bug in DataFrame construction from nested dict with timedelta keys (GH11129)
  • Bug in .fillna against may raise TypeError when data contains datetime dtype (GH7095, GH11153)
  • Bug in .groupby when number of keys to group by is same as length of index (GH11185)
  • Bug in convert_objects where converted values might not be returned if all null and coerce (GH9589)
  • Bug in convert_objects where copy keyword was not respected (GH9589)

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