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# Version 0.19.1 (November 3, 2016)

This is a minor bug-fix release from 0.19.0 and includes some small regression fixes, bug fixes and performance improvements. We recommend that all users upgrade to this version.

## Performance improvements

- Fixed performance regression in factorization of `Period` data (GH 14338)

- Fixed performance regression in `Series.asof(where)` when `where` is a scalar (GH 14461)

- Improved performance in `DataFrame.asof(where)` when `where` is a scalar (GH 14461)

- Improved performance in `.to_json()` when `lines=True` (GH 14408)

- Improved performance in certain types of `loc` indexing with a MultiIndex (GH 14551).

## Bug fixes

- Source installs from PyPI will now again work without `cython` installed, as in previous versions (GH 14204)

- Compat with Cython 0.25 for building (GH 14496)

- Fixed regression where user-provided file handles were closed in `read_csv` (c engine) (GH 14418).

- Fixed regression in `DataFrame.quantile` when missing values where present in some columns (GH 14357).

- Fixed regression in `Index.difference` where the `freq` of a `DatetimeIndex` was incorrectly set (GH 14323)

- Added back `pandas.core.common.array_equivalent` with a deprecation warning (GH 14555).

- Bug in `pd.read_csv` for the C engine in which quotation marks were improperly parsed in skipped rows (GH 14459)

- Bug in `pd.read_csv` for Python 2.x in which Unicode quote characters were no longer being respected (GH 14477)

- Fixed regression in `Index.append` when categorical indices were appended (GH 14545).

- Fixed regression in `pd.DataFrame` where constructor fails when given dict with `None` value (GH 14381)

- Fixed regression in `DatetimeIndex._maybe_cast_slice_bound` when index is empty (GH 14354).

- Bug in localizing an ambiguous timezone when a boolean is passed (GH 14402)

- Bug in `TimedeltaIndex` addition with a Datetime-like object where addition overflow in the negative direction was not being caught (GH 14068, GH 14453)

- Bug in string indexing against data with `object` `Index` may raise `AttributeError` (GH 14424)

- Correctly raise `ValueError` on empty input to `pd.eval()` and `df.query()` (GH 13139)

- Bug in `RangeIndex.intersection` when result is a empty set (GH 14364).

- Bug in groupby-transform broadcasting that could cause incorrect dtype coercion (GH 14457)

- Bug in `Series.__setitem__` which allowed mutating read-only arrays (GH 14359).

- Bug in `DataFrame.insert` where multiple calls with duplicate columns can fail (GH 14291)

- `pd.merge()` will raise `ValueError` with non-boolean parameters in passed boolean type arguments (GH 14434)

- Bug in `Timestamp` where dates very near the minimum (1677-09) could underflow on creation (GH 14415)

- Bug in `pd.concat` where names of the `keys` were not propagated to the resulting `MultiIndex` (GH 14252)

- Bug in `pd.concat` where `axis` cannot take string parameters `'rows'` or `'columns'` (GH 14369)

- Bug in `pd.concat` with dataframes heterogeneous in length and tuple `keys` (GH 14438)

- Bug in `MultiIndex.set_levels` where illegal level values were still set after raising an error (GH 13754)

- Bug in `DataFrame.to_json` where `lines=True` and a value contained a `}` character (GH 14391)

- Bug in `df.groupby` causing an `AttributeError` when grouping a single index frame by a column and the index level (GH 14327)

- Bug in `df.groupby` where `TypeError` raised when `pd.Grouper(key=...)` is passed in a list (GH 14334)

- Bug in `pd.pivot_table` may raise `TypeError` or `ValueError` when `index` or `columns` is not scalar and `values` is not specified (GH 14380)

## Contributors

A total of 30 people contributed patches to this release. People with a “+” by their names contributed a patch for the first time.

- Adam Chainz +

- Anthonios Partheniou

- Arash Rouhani +

- Ben Kandel

- Brandon M. Burroughs +

- Chris

- Chris Warth

- David Krych +

- Iván Vallés Pérez +

- Jeff Reback

- Joe Jevnik

- Jon M. Mease +

- Jon Mease +

- Joris Van den Bossche

- Josh Owen +

- Keshav Ramaswamy +

- Larry Ren +

- Michael Felt +

- Piotr Chromiec +

- Robert Bradshaw +

- Sinhrks

- Thiago Serafim +

- Tom Bird

- bkandel +

- chris-b1

- dubourg +

- gfyoung

- mattrijk +

- paul-mannino +

- sinhrks