You can pass a function that parses the correct format to the date_parser kwarg of read_csv, but another option is also to not parse the dates when reading, but afterwards with to_datetime (this functions allows to specify a format):

df = pd.read_csv('file.txt', sep=' ', header=None, index_col=0, names= ('C1', 'C2', 'C3', 'C4'), use_unsigned=True) df['date_col'] = pd.to_datetime(df['date_col'], format="%Y-%m-%d-%H-%M-%S") 

You can pass a function that parses the correct format to the date_parser kwarg of read_csv, but another option is to not parse the dates when reading, but afterwards with to_datetime (this functions allows to specify a format, and will be faster than a custom date_parser function):

df = pd.read_csv('file.txt', sep=' ', header=None, index_col=0, names= ('C1', 'C2', 'C3', 'C4'), use_unsigned=True) df.index = pd.to_datetime(df.index, format="%Y-%m-%d-%H-%M-%S")