[Python] Implement casts from timestamp to date32/date64 and support in Array.from_pandas

[asfimport]

When calling Array.from_pandas with a pandas.Series of dates and specifying the desired pyarrow type, an error occurs. If the type is not specified then from_pandas will interpret the data as a timestamp type.

import pandas as pd
import pyarrow as pa
import datetime

arr = pa.array([datetime.date(2017, 10, 23)])
c = pa.Column.from_array("d", arr)

s = c.to_pandas()
print(s)
# 0   2017-10-23
# Name: d, dtype: datetime64[ns]

result = pa.Array.from_pandas(s, type=pa.date32())
print(result)
"""
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "pyarrow/array.pxi", line 295, in pyarrow.lib.Array.__repr__ (/home/bryan/git/arrow/python/build/temp.linux-x86_64-2.7/lib.cxx:26221)
  File "/home/bryan/.local/lib/python2.7/site-packages/pyarrow-0.7.2.dev21+ng028f2cd-py2.7-linux-x86_64.egg/pyarrow/formatting.py", line 28, in array_format
    values.append(value_format(x, 0))
  File "/home/bryan/.local/lib/python2.7/site-packages/pyarrow-0.7.2.dev21+ng028f2cd-py2.7-linux-x86_64.egg/pyarrow/formatting.py", line 49, in value_format
    return repr(x)
  File "pyarrow/scalar.pxi", line 63, in pyarrow.lib.ArrayValue.__repr__ (/home/bryan/git/arrow/python/build/temp.linux-x86_64-2.7/lib.cxx:19535)
  File "pyarrow/scalar.pxi", line 137, in pyarrow.lib.Date32Value.as_py (/home/bryan/git/arrow/python/build/temp.linux-x86_64-2.7/lib.cxx:20368)
ValueError: year is out of range
"""

Reporter: Bryan Cutler / @BryanCutler
Assignee: Wes McKinney / @wesm

Related issues:

• [Python] Timestamp unit change not done in from_pandas() conversion (is related to)

PRs and other links:

• GitHub Pull Request #1258

_{Note: This issue was originally created as ARROW-1718. Please see the migration documentation for further details.}

[asfimport]

Bryan Cutler / @BryanCutler:
@wesm I am also wondering if Column.to_pandas from the code above should produce a 'datetime64[ns]' series? I believe Array.to_pandas creates a 'datetime64[D]' series.

[asfimport]

Wes McKinney / @wesm:
That sounds inconsistent. Will have to take a closer look

[asfimport]

Wes McKinney / @wesm:
There's a bit of work to do here but it will be for the greater good. I changed the title to reflect the scope of the work (which is more than a bugfix). Should have a patch out in the next few days

[asfimport]

Uwe Korn / @xhochy:
Issue resolved by pull request 1258
#1258