python - Create Empty Dataframe in Pandas specifying column types

Question

I'm trying to create an empty data frame with an index and specify the column types. The way I am doing it is the following:

df = pd.DataFrame(index=['pbp'],
                  columns=['contract',
                           'state_and_county_code',
                           'state',
                           'county',
                           'starting_membership',
                           'starting_raw_raf',
                           'enrollment_trend',
                           'projected_membership',
                           'projected_raf'],
                  dtype=['str', 'str', 'str', 'str',
                         'int', 'float', 'float',
                         'int', 'float'])

However, I get the following error,

TypeError: data type not understood

What does this mean?

Answer 1

You can use the following:

df = pd.DataFrame({'a': pd.Series(dtype='int'),
                   'b': pd.Series(dtype='str'),
                   'c': pd.Series(dtype='float')})

or more abstractly:

df = pd.DataFrame({c: pd.Series(dtype=t) for c, t in {'a': 'int', 'b': 'str', 'c': 'float'}.items()})

then if you call df you have:

>>> df 
Empty DataFrame 
Columns: [a, b, c]
Index: []

and if you check its types:

>>> df.dtypes
a      int32
b     object
c    float64
dtype: object