Actual dtypes of pd.DataFrame(None, [...], dtype=int)

[toobaz]

Code Sample, a copy-pastable example if possible

In [2]: pd.DataFrame(index=range(2), columns=['a', 'b'], dtype=int).dtypes
Out[2]: 
a    object
b    object
dtype: object

compare to

In [3]: pd.Series(index=range(2), dtype=int).dtype
Out[3]: dtype('float64')

Problem description

See #18600 (comment)

Wrong test in

pandas/pandas/tests/frame/test_constructors.py

Line 738 in 324379c

assert df.values.dtype == np.object_

Fixed by #18600

Output of pd.show_versions()

INSTALLED VERSIONS ------------------ commit: 5052842 python: 3.5.3.final.0 python-bits: 64 OS: Linux OS-release: 4.9.0-5-amd64 machine: x86_64 processor: byteorder: little LC_ALL: None LANG: it_IT.UTF-8 LOCALE: it_IT.UTF-8

pandas: 0.23.0.dev0+248.g50528421a
pytest: 3.2.3
pip: 9.0.1
setuptools: 36.7.0
Cython: 0.25.2
numpy: 1.12.1
scipy: 0.19.0
pyarrow: None
xarray: None
IPython: 6.2.1
sphinx: 1.5.6
patsy: 0.4.1
dateutil: 2.6.1
pytz: 2017.2
blosc: None
bottleneck: 1.2.0dev
tables: 3.3.0
numexpr: 2.6.1
feather: 0.3.1
matplotlib: 2.0.0
openpyxl: 2.3.0
xlrd: 1.0.0
xlwt: 1.3.0
xlsxwriter: 0.9.6
lxml: 4.1.1
bs4: 4.5.3
html5lib: 0.999999999
sqlalchemy: 1.0.15
pymysql: None
psycopg2: None
jinja2: 2.10
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: 0.2.1