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# Version 0.12.0 (July 24, 2013)

This is a major release from 0.11.0 and includes several new features and enhancements along with a large number of bug fixes.

Highlights include a consistent I/O API naming scheme, routines to read html, write MultiIndexes to csv files, read & write STATA data files, read & write JSON format files, Python 3 support for `HDFStore`, filtering of groupby expressions via `filter`, and a revamped `replace` routine that accepts regular expressions.

## API changes

> - The I/O API is now much more consistent with a set of top level `reader` functions accessed like `pd.read_csv()` that generally return a `pandas` object.

>   - `read_csv`

>   - `read_excel`

>   - `read_hdf`

>   - `read_sql`

>   - `read_json`

>   - `read_html`

>   - `read_stata`

>   - `read_clipboard`

>   The corresponding `writer` functions are object methods that are accessed like `df.to_csv()`

>   - `to_csv`

>   - `to_excel`

>   - `to_hdf`

>   - `to_sql`

>   - `to_json`

>   - `to_html`

>   - `to_stata`

>   - `to_clipboard`

> - Fix modulo and integer division on Series,DataFrames to act similarly to `float` dtypes to return `np.nan` or `np.inf` as appropriate (GH 3590). This correct a numpy bug that treats `integer` and `float` dtypes differently.

>       In [1]: p = pd.DataFrame({"first": [4, 5, 8], "second": [0, 0, 3]})

>       In [2]: p % 0
>       Out[2]:
>          first  second
>       0    NaN     NaN
>       1    NaN     NaN
>       2    NaN     NaN

>       In [3]: p % p
>       Out[3]:
>          first  second
>       0    0.0     NaN
>       1    0.0     NaN
>       2    0.0     0.0

>       In [4]: p / p
>       Out[4]:
>          first  second
>       0    1.0     NaN
>       1    1.0     NaN
>       2    1.0     1.0

>       In [5]: p / 0
>       Out[5]:
>          first  second
>       0    inf     NaN
>       1    inf     NaN
>       2    inf     inf

> - Add `squeeze` keyword to `groupby` to allow reduction from DataFrame -> Series if groups are unique. This is a Regression from 0.10.1. We are reverting back to the prior behavior. This means groupby will return the same shaped objects whether the groups are unique or not. Revert this issue (GH 2893) with (GH 3596).

>       In [2]: df2 = pd.DataFrame([{"val1": 1, "val2": 20},
>          ...:                     {"val1": 1, "val2": 19},
>          ...:                     {"val1": 1, "val2": 27},
>          ...:                     {"val1": 1, "val2": 12}])

>       In [3]: def func(dataf):
>          ...:     return dataf["val2"] - dataf["val2"].mean()
>          ...:

>       In [4]: # squeezing the result frame to a series (because we have unique groups)
>          ...: df2.groupby("val1", squeeze=True).apply(func)
>       Out[4]:
>       0    0.5
>       1   -0.5
>       2    7.5
>       3   -7.5
>       Name: 1, dtype: float64

>       In [5]: # no squeezing (the default, and behavior in 0.10.1)
>          ...: df2.groupby("val1").apply(func)
>       Out[5]:
>       val2    0    1    2    3
>       val1
>       1     0.5 -0.5  7.5 -7.5

> - Raise on `iloc` when boolean indexing with a label based indexer mask e.g. a boolean Series, even with integer labels, will raise. Since `iloc` is purely positional based, the labels on the Series are not alignable (GH 3631)

>   This case is rarely used, and there are plenty of alternatives. This preserves the `iloc` API to be purely positional based.

>       In [6]: df = pd.DataFrame(range(5), index=list("ABCDE"), columns=["a"])

>       In [7]: mask = df.a % 2 == 0

>       In [8]: mask
>       Out[8]:
>       A     True
>       B    False
>       C     True
>       D    False
>       E     True
>       Name: a, dtype: bool

>       # this is what you should use
>       In [9]: df.loc[mask]
>       Out[9]:
>          a
>       A  0
>       C  2
>       E  4

>       # this will work as well
>       In [10]: df.iloc[mask.values]
>       Out[10]:
>          a
>       A  0
>       C  2
>       E  4

>   `df.iloc[mask]` will raise a `ValueError`

> - The `raise_on_error` argument to plotting functions is removed. Instead, plotting functions raise a `TypeError` when the `dtype` of the object is `object` to remind you to avoid `object` arrays whenever possible and thus you should cast to an appropriate numeric dtype if you need to plot something.

> - Add `colormap` keyword to DataFrame plotting methods. Accepts either a matplotlib colormap object (ie, matplotlib.cm.jet) or a string name of such an object (ie, ‘jet’). The colormap is sampled to select the color for each column. Please see Colormaps for more information. (GH 3860)

> - `DataFrame.interpolate()` is now deprecated. Please use `DataFrame.fillna()` and `DataFrame.replace()` instead. (GH 3582, GH 3675, GH 3676)

> - the `method` and `axis` arguments of `DataFrame.replace()` are deprecated

> - `DataFrame.replace` ‘s `infer_types` parameter is removed and now performs conversion by default. (GH 3907)

> - Add the keyword `allow_duplicates` to `DataFrame.insert` to allow a duplicate column to be inserted if `True`, default is `False` (same as prior to 0.12) (GH 3679)

> - Implement `__nonzero__` for `NDFrame` objects (GH 3691, GH 3696)

> - IO API

>   - Added top-level function `read_excel` to replace the following, The original API is deprecated and will be removed in a future version

>         from pandas.io.parsers import ExcelFile

>         xls = ExcelFile("path_to_file.xls")
>         xls.parse("Sheet1", index_col=None, na_values=["NA"])

>     With

>         import pandas as pd

>         pd.read_excel("path_to_file.xls", "Sheet1", index_col=None, na_values=["NA"])

>   - Added top-level function `read_sql` that is equivalent to the following

>         from pandas.io.sql import read_frame

>         read_frame(...)

> - `DataFrame.to_html` and `DataFrame.to_latex` now accept a path for their first argument (GH 3702)

> - Do not allow astypes on `datetime64[ns]` except to `object`, and `timedelta64[ns]` to `object/int` (GH 3425)

> - The behavior of `datetime64` dtypes has changed with respect to certain so-called reduction operations (GH 3726). The following operations now raise a `TypeError` when performed on a `Series` and return an empty `Series` when performed on a `DataFrame` similar to performing these operations on, for example, a `DataFrame` of `slice` objects:

>   - sum, prod, mean, std, var, skew, kurt, corr, and cov

> - `read_html` now defaults to `None` when reading, and falls back on `bs4` + `html5lib` when lxml fails to parse. a list of parsers to try until success is also valid

> - The internal `pandas` class hierarchy has changed (slightly). The previous `PandasObject` now is called `PandasContainer` and a new `PandasObject` has become the base class for `PandasContainer` as well as `Index`, `Categorical`, `GroupBy`, `SparseList`, and `SparseArray` (+ their base classes). Currently, `PandasObject` provides string methods (from `StringMixin`). (GH 4090, GH 4092)

> - New `StringMixin` that, given a `__unicode__` method, gets python 2 and python 3 compatible string methods (`__str__`, `__bytes__`, and `__repr__`). Plus string safety throughout. Now employed in many places throughout the pandas library. (GH 4090, GH 4092)

## IO enhancements

> - `pd.read_html()` can now parse HTML strings, files or urls and return DataFrames, courtesy of @cpcloud. (GH 3477, GH 3605, GH 3606, GH 3616). It works with a single parser backend: BeautifulSoup4 + html5lib See the docs

>   You can use `pd.read_html()` to read the output from `DataFrame.to_html()` like so

>       In [11]: import io

>       In [12]: df = pd.DataFrame({"a": range(3), "b": list("abc")})

>       In [13]: print(df)
>          a  b
>       0  0  a
>       1  1  b
>       2  2  c

>       In [14]: html = df.to_html()

>       In [15]: alist = pd.read_html(io.StringIO(html), index_col=0)

>       In [16]: print(df == alist[0])
>             a     b
>       0  True  True
>       1  True  True
>       2  True  True

>   Note that `alist` here is a Python `list` so `pd.read_html()` and `DataFrame.to_html()` are not inverses.

>   - `pd.read_html()` no longer performs hard conversion of date strings (GH 3656).

>   Warning

>   You may have to install an older version of BeautifulSoup4, See the installation docs

> - Added module for reading and writing Stata files: `pandas.io.stata` (GH 1512) accessible via `read_stata` top-level function for reading, and `to_stata` DataFrame method for writing, See the docs

> - Added module for reading and writing json format files: `pandas.io.json` accessible via `read_json` top-level function for reading, and `to_json` DataFrame method for writing, See the docs various issues (GH 1226, GH 3804, GH 3876, GH 3867, GH 1305)

> - `MultiIndex` column support for reading and writing csv format files

>   - The `header` option in `read_csv` now accepts a list of the rows from which to read the index.

>   - The option, `tupleize_cols` can now be specified in both `to_csv` and `read_csv`, to provide compatibility for the pre 0.12 behavior of writing and reading `MultIndex` columns via a list of tuples. The default in 0.12 is to write lists of tuples and not interpret list of tuples as a `MultiIndex` column.

>     Note: The default behavior in 0.12 remains unchanged from prior versions, but starting with 0.13, the default to write and read `MultiIndex` columns will be in the new format. (GH 3571, GH 1651, GH 3141)

>   - If an `index_col` is not specified (e.g. you don’t have an index, or wrote it with `df.to_csv(..., index=False)`), then any `names` on the columns index will be lost.

>         In [17]: mi_idx = pd.MultiIndex.from_arrays([[1, 2, 3, 4], list("abcd")], names=list("ab"))

>         In [18]: mi_col = pd.MultiIndex.from_arrays([[1, 2], list("ab")], names=list("cd"))

>         In [19]: df = pd.DataFrame(np.ones((4, 2)), index=mi_idx, columns=mi_col)

>         In [20]: df.to_csv("mi.csv")

>         In [21]: print(open("mi.csv").read())
>         c,,1,2
>         d,,a,b
>         a,b,,
>         1,a,1.0,1.0
>         2,b,1.0,1.0
>         3,c,1.0,1.0
>         4,d,1.0,1.0

>         In [22]: pd.read_csv("mi.csv", header=[0, 1, 2, 3], index_col=[0, 1])
>         Out[22]:
>         c                    1                  2
>         d                    a                  b
>         a   Unnamed: 2_level_2 Unnamed: 3_level_2
>         1                  1.0                1.0
>         2 b                1.0                1.0
>         3 c                1.0                1.0
>         4 d                1.0                1.0

> - Support for `HDFStore` (via `PyTables 3.0.0`) on Python3

> - Iterator support via `read_hdf` that automatically opens and closes the store when iteration is finished. This is only for tables

>       In [25]: path = 'store_iterator.h5'

>       In [26]: pd.DataFrame(np.random.randn(10, 2)).to_hdf(path, 'df', table=True)

>       In [27]: for df in pd.read_hdf(path, 'df', chunksize=3):
>          ....:     print(df)
>          ....:
>                 0         1
>       0  0.713216 -0.778461
>       1 -0.661062  0.862877
>       2  0.344342  0.149565
>                 0         1
>       3 -0.626968 -0.875772
>       4 -0.930687 -0.218983
>       5  0.949965 -0.442354
>                 0         1
>       6 -0.402985  1.111358
>       7 -0.241527 -0.670477
>       8  0.049355  0.632633
>                 0         1
>       9 -1.502767 -1.225492

> - `read_csv` will now throw a more informative error message when a file contains no columns, e.g., all newline characters

## Other enhancements

> - `DataFrame.replace()` now allows regular expressions on contained `Series` with object dtype. See the examples section in the regular docs Replacing via String Expression

>   For example you can do

>       In [23]: df = pd.DataFrame({"a": list("ab.."), "b": [1, 2, 3, 4]})

>       In [24]: df.replace(regex=r"\s*\.\s*", value=np.nan)
>       Out[24]:
>            a  b
>       0    a  1
>       1    b  2
>       2  NaN  3
>       3  NaN  4

>   to replace all occurrences of the string `'.'` with zero or more instances of surrounding white space with `NaN`.

>   Regular string replacement still works as expected. For example, you can do

>       In [25]: df.replace(".", np.nan)
>       Out[25]:
>            a  b
>       0    a  1
>       1    b  2
>       2  NaN  3
>       3  NaN  4

>   to replace all occurrences of the string `'.'` with `NaN`.

> - `pd.melt()` now accepts the optional parameters `var_name` and `value_name` to specify custom column names of the returned DataFrame.

> - `pd.set_option()` now allows N option, value pairs (GH 3667).

>   Let’s say that we had an option `'a.b'` and another option `'b.c'`. We can set them at the same time:

>       In [31]: pd.get_option('a.b')
>       Out[31]: 2

>       In [32]: pd.get_option('b.c')
>       Out[32]: 3

>       In [33]: pd.set_option('a.b', 1, 'b.c', 4)

>       In [34]: pd.get_option('a.b')
>       Out[34]: 1

>       In [35]: pd.get_option('b.c')
>       Out[35]: 4

> - The `filter` method for group objects returns a subset of the original object. Suppose we want to take only elements that belong to groups with a group sum greater than 2.

>       In [26]: sf = pd.Series([1, 1, 2, 3, 3, 3])

>       In [27]: sf.groupby(sf).filter(lambda x: x.sum() > 2)
>       Out[27]:
>       3    3
>       4    3
>       5    3
>       dtype: int64

>   The argument of `filter` must a function that, applied to the group as a whole, returns `True` or `False`.

>   Another useful operation is filtering out elements that belong to groups with only a couple members.

>       In [28]: dff = pd.DataFrame({"A": np.arange(8), "B": list("aabbbbcc")})

>       In [29]: dff.groupby("B").filter(lambda x: len(x) > 2)
>       Out[29]:
>          A  B
>       2  2  b
>       3  3  b
>       4  4  b
>       5  5  b

>   Alternatively, instead of dropping the offending groups, we can return a like-indexed objects where the groups that do not pass the filter are filled with NaNs.

>       In [30]: dff.groupby("B").filter(lambda x: len(x) > 2, dropna=False)
>       Out[30]:
>            A    B
>       0  NaN  NaN
>       1  NaN  NaN
>       2  2.0    b
>       3  3.0    b
>       4  4.0    b
>       5  5.0    b
>       6  NaN  NaN
>       7  NaN  NaN

> - Series and DataFrame hist methods now take a `figsize` argument (GH 3834)

> - DatetimeIndexes no longer try to convert mixed-integer indexes during join operations (GH 3877)

> - Timestamp.min and Timestamp.max now represent valid Timestamp instances instead of the default datetime.min and datetime.max (respectively), thanks @SleepingPills

> - `read_html` now raises when no tables are found and BeautifulSoup==4.2.0 is detected (GH 4214)

## Experimental features

> - Added experimental `CustomBusinessDay` class to support `DateOffsets` with custom holiday calendars and custom weekmasks. (GH 2301)

>   Note

>   This uses the `numpy.busdaycalendar` API introduced in Numpy 1.7 and therefore requires Numpy 1.7.0 or newer.

>       In [31]: from pandas.tseries.offsets import CustomBusinessDay

>       In [32]: from datetime import datetime

>       # As an interesting example, let's look at Egypt where
>       # a Friday-Saturday weekend is observed.
>       In [33]: weekmask_egypt = "Sun Mon Tue Wed Thu"

>       # They also observe International Workers' Day so let's
>       # add that for a couple of years
>       In [34]: holidays = ["2012-05-01", datetime(2013, 5, 1), np.datetime64("2014-05-01")]

>       In [35]: bday_egypt = CustomBusinessDay(holidays=holidays, weekmask=weekmask_egypt)

>       In [36]: dt = datetime(2013, 4, 30)

>       In [37]: print(dt + 2 * bday_egypt)
>       2013-05-05 00:00:00

>       In [38]: dts = pd.date_range(dt, periods=5, freq=bday_egypt)

>       In [39]: print(pd.Series(dts.weekday, dts).map(pd.Series("Mon Tue Wed Thu Fri Sat Sun".split())))
>       2013-04-30    Tue
>       2013-05-02    Thu
>       2013-05-05    Sun
>       2013-05-06    Mon
>       2013-05-07    Tue
>       Freq: C, dtype: str

## Bug fixes

> - Plotting functions now raise a `TypeError` before trying to plot anything if the associated objects have a dtype of `object` (GH 1818, GH 3572, GH 3911, GH 3912), but they will try to convert object arrays to numeric arrays if possible so that you can still plot, for example, an object array with floats. This happens before any drawing takes place which eliminates any spurious plots from showing up.

> - `fillna` methods now raise a `TypeError` if the `value` parameter is a list or tuple.

> - `Series.str` now supports iteration (GH 3638). You can iterate over the individual elements of each string in the `Series`. Each iteration yields a `Series` with either a single character at each index of the original `Series` or `NaN`. For example,

>       In [38]: strs = "go", "bow", "joe", "slow"

>       In [32]: ds = pd.Series(strs)

>       In [33]: for s in ds.str:
>           ...:     print(s)

>       0    g
>       1    b
>       2    j
>       3    s
>       dtype: object
>       0    o
>       1    o
>       2    o
>       3    l
>       dtype: object
>       0    NaN
>       1      w
>       2      e
>       3      o
>       dtype: object
>       0    NaN
>       1    NaN
>       2    NaN
>       3      w
>       dtype: object

>       In [41]: s
>       Out[41]:
>       0    NaN
>       1    NaN
>       2    NaN
>       3      w
>       dtype: object

>       In [42]: s.dropna().values.item() == "w"
>       Out[42]: True

>   The last element yielded by the iterator will be a `Series` containing the last element of the longest string in the `Series` with all other elements being `NaN`. Here since `'slow'` is the longest string and there are no other strings with the same length `'w'` is the only non-null string in the yielded `Series`.

> - `HDFStore`

>   - Will retain index attributes (freq,tz,name) on recreation (GH 3499)

>   - Will warn with a `AttributeConflictWarning` if you are attempting to append an index with a different frequency than the existing, or attempting to append an index with a different name than the existing

>   - Support datelike columns with a timezone as data_columns (GH 2852)

> - Non-unique index support clarified (GH 3468).

>   - Fix assigning a new index to a duplicate index in a DataFrame would fail (GH 3468)

>   - Fix construction of a DataFrame with a duplicate index

>   - ref_locs support to allow duplicative indices across dtypes, allows iget support to always find the index (even across dtypes) (GH 2194)

>   - applymap on a DataFrame with a non-unique index now works (removed warning) (GH 2786), and fix (GH 3230)

>   - Fix to_csv to handle non-unique columns (GH 3495)

>   - Duplicate indexes with getitem will return items in the correct order (GH 3455, GH 3457) and handle missing elements like unique indices (GH 3561)

>   - Duplicate indexes with and empty DataFrame.from_records will return a correct frame (GH 3562)

>   - Concat to produce a non-unique columns when duplicates are across dtypes is fixed (GH 3602)

>   - Allow insert/delete to non-unique columns (GH 3679)

>   - Non-unique indexing with a slice via `loc` and friends fixed (GH 3659)

>   - Allow insert/delete to non-unique columns (GH 3679)

>   - Extend `reindex` to correctly deal with non-unique indices (GH 3679)

>   - `DataFrame.itertuples()` now works with frames with duplicate column names (GH 3873)

>   - Bug in non-unique indexing via `iloc` (GH 4017); added `takeable` argument to `reindex` for location-based taking

>   - Allow non-unique indexing in series via `.ix/.loc` and `__getitem__` (GH 4246)

>   - Fixed non-unique indexing memory allocation issue with `.ix/.loc` (GH 4280)

> - `DataFrame.from_records` did not accept empty recarrays (GH 3682)

> - `read_html` now correctly skips tests (GH 3741)

> - Fixed a bug where `DataFrame.replace` with a compiled regular expression in the `to_replace` argument wasn’t working (GH 3907)

> - Improved `network` test decorator to catch `IOError` (and therefore `URLError` as well). Added `with_connectivity_check` decorator to allow explicitly checking a website as a proxy for seeing if there is network connectivity. Plus, new `optional_args` decorator factory for decorators. (GH 3910, GH 3914)

> - Fixed testing issue where too many sockets where open thus leading to a connection reset issue (GH 3982, GH 3985, GH 4028, GH 4054)

> - Fixed failing tests in test_yahoo, test_google where symbols were not retrieved but were being accessed (GH 3982, GH 3985, GH 4028, GH 4054)

> - `Series.hist` will now take the figure from the current environment if one is not passed

> - Fixed bug where a 1xN DataFrame would barf on a 1xN mask (GH 4071)

> - Fixed running of `tox` under python3 where the pickle import was getting rewritten in an incompatible way (GH 4062, GH 4063)

> - Fixed bug where sharex and sharey were not being passed to grouped_hist (GH 4089)

> - Fixed bug in `DataFrame.replace` where a nested dict wasn’t being iterated over when regex=False (GH 4115)

> - Fixed bug in the parsing of microseconds when using the `format` argument in `to_datetime` (GH 4152)

> - Fixed bug in `PandasAutoDateLocator` where `invert_xaxis` triggered incorrectly `MilliSecondLocator` (GH 3990)

> - Fixed bug in plotting that wasn’t raising on invalid colormap for matplotlib 1.1.1 (GH 4215)

> - Fixed the legend displaying in `DataFrame.plot(kind='kde')` (GH 4216)

> - Fixed bug where Index slices weren’t carrying the name attribute (GH 4226)

> - Fixed bug in initializing `DatetimeIndex` with an array of strings in a certain time zone (GH 4229)

> - Fixed bug where html5lib wasn’t being properly skipped (GH 4265)

> - Fixed bug where get_data_famafrench wasn’t using the correct file edges (GH 4281)

See the full release notes or issue tracker on GitHub for a complete list.

## Contributors

A total of 50 people contributed patches to this release. People with a “+” by their names contributed a patch for the first time.

- Andy Hayden

- Chang She

- Christopher Whelan

- Damien Garaud

- Dan Allan

- Dan Birken

- Dieter Vandenbussche

- Dražen Lučanin

- Gábor Lipták +

- Jeff Mellen +

- Jeff Tratner +

- Jeffrey Tratner +

- Jonathan deWerd +

- Joris Van den Bossche +

- Juraj Niznan +

- Karmel Allison

- Kelsey Jordahl

- Kevin Stone +

- Kieran O’Mahony

- Kyle Meyer +

- Mike Kelly +

- PKEuS +

- Patrick O’Brien +

- Phillip Cloud

- Richard Höchenberger +

- Skipper Seabold

- SleepingPills +

- Tobias Brandt

- Tom Farnbauer +

- TomAugspurger +

- Trent Hauck +

- Wes McKinney

- Wouter Overmeire

- Yaroslav Halchenko

- conmai +

- danielballan +

- davidshinn +

- dieterv77

- duozhang +

- ejnens +

- gliptak +

- jniznan +

- jreback

- lexual

- nipunreddevil +

- ogiaquino +

- stonebig +

- tim smith +

- timmie

- y-p