# v0.19.1 (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.

What’s new in v0.19.1

- Performance improvements
- Bug fixes
- Contributors

## Performance improvements

- Fixed performance regression in factorization of `Period` data (GH14338)
- Fixed performance regression in `Series.asof(where)` when `where` is a scalar (GH14461)
- Improved performance in `DataFrame.asof(where)` when `where` is a scalar (GH14461)
- Improved performance in `.to_json()` when `lines=True` (GH14408)
- Improved performance in certain types of loc indexing with a MultiIndex (GH14551).

## Bug fixes

- Source installs from PyPI will now again work without `cython` installed, as in previous versions (GH14204)
- Compat with Cython 0.25 for building (GH14496)
- Fixed regression where user-provided file handles were closed in `read_csv` (c engine) (GH14418).
- Fixed regression in `DataFrame.quantile` when missing values where present in some columns (GH14357).
- Fixed regression in `Index.difference` where the `freq` of a `DatetimeIndex` was incorrectly set (GH14323)
- Added back `pandas.core.common.array_equivalent` with a deprecation warning (GH14555).
- Bug in `pd.read_csv` for the C engine in which quotation marks were improperly parsed in skipped rows (GH14459)
- Bug in `pd.read_csv` for Python 2.x in which Unicode quote characters were no longer being respected (GH14477)
- Fixed regression in `Index.append` when categorical indices were appended (GH14545).
- Fixed regression in `pd.DataFrame` where constructor fails when given dict with `None` value (GH14381)
- Fixed regression in `DatetimeIndex._maybe_cast_slice_bound` when index is empty (GH14354).
- Bug in localizing an ambiguous timezone when a boolean is passed (GH14402)
- Bug in `TimedeltaIndex` addition with a Datetime-like object where addition overflow in the negative direction was not being caught (GH14068, GH14453)
- Bug in string indexing against data with `object` `Index` may raise `AttributeError` (GH14424)
- Correctly raise `ValueError` on empty input to `pd.eval()` and `df.query()` (GH13139)
- Bug in `RangeIndex.intersection` when result is a empty set (GH14364).
- Bug in groupby-transform broadcasting that could cause incorrect dtype coercion (GH14457)
- Bug in `Series.__setitem__` which allowed mutating read-only arrays (GH14359).
- Bug in `DataFrame.insert` where multiple calls with duplicate columns can fail (GH14291)
- `pd.merge()` will raise `ValueError` with non-boolean parameters in passed boolean type arguments (GH14434)
- Bug in `Timestamp` where dates very near the minimum (1677-09) could underflow on creation (GH14415)
- Bug in `pd.concat` where names of the `keys` were not propagated to the resulting `MultiIndex` (GH14252)
- Bug in `pd.concat` where `axis` cannot take string parameters `'rows'` or `'columns'` (GH14369)
- Bug in `pd.concat` with dataframes heterogeneous in length and tuple `keys` (GH14438)
- Bug in `MultiIndex.set_levels` where illegal level values were still set after raising an error (GH13754)
- Bug in `DataFrame.to_json` where `lines=True` and a value contained a `}` character (GH14391)
- Bug in `df.groupby` causing an `AttributeError` when grouping a single index frame by a column and the index level (GH14327)
- Bug in `df.groupby` where `TypeError` raised when `pd.Grouper(key=...)` is passed in a list (GH14334)
- Bug in `pd.pivot_table` may raise `TypeError` or `ValueError` when `index` or `columns` is not scalar and `values` is not specified (GH14380)

## Contributors

For contributors, please see /usr/share/doc/contributors_list.txt or https://github.com/pandas-dev/pandas/graphs/contributors
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