DataFrame constructor ignores integer dtype when dict-data and non-overlapping columns

[TomAugspurger]

This is close to #24385, but we don't have a test saying otherwise, so I'm actually going to fix this one :)

In [21]: pd.DataFrame({"a": [1, 2]}, columns=['b'], dtype=int).dtypes
Out[21]:
b    float64
dtype: object

In [22]: pd.DataFrame({"a": [1, 2]}, columns=['b'], dtype='datetime64[ns]').dtypes
Out[22]:
b    datetime64[ns]
dtype: object

Out[21] should be int64.

[chengsoonong]

It also seems to happen when constructing using index and columns only (no data).

pd.DataFrame(index=[0], columns=['b'], dtype=int).dtypes

returns

b    float64
dtype: object

[mroeschke]

This looks to be fixed on master. Could use a test

In [17]: In [21]: pd.DataFrame({"a": [1, 2]}, columns=['b'], dtype=int).dtypes
Out[17]:
b    int64
dtype: object

In [18]: pd.__version__
Out[18]: '1.1.0.dev0+1313.g1c0cc62e3'

[avinashpancham]

take