change dataframe column type

# You can use "astype" method
# suppose you want to correct your "sales" column data type
df['sales'] = df['sales'].astype('float64')

>>> df.astype({'col1': 'int32'}).dtypes
col1    int32
col2    int64
dtype: object

df = pd.read_csv("weather.tsv", sep="\t",  
                 dtype={'Day': str,'Wind':int64})
df.dtypes