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[python] Determine if the string is a number (including decimals)


What I want to do


I want to determine if a given string is a number.



Problem


Python has a method called isnumeric () that determines whether a string is a number, but if it is a decimal, "." is regarded as a character.

"1".isnumeric()   
# True

"1.2".isnumeric()   
# False


Solution


There seems to be no method to judge the decimal number, so I will make it myself.

Cast with float (), and if an exception occurs, judge it as a character string.

def is_float(x):
    
    try:
        y=float(x)
        return True
    except:
        return False
is_float("1.2")
# True

is_float("a")
# False


Application


I ran into this problem while reading and processing data from a csv file. It was a "dirty" data file where the part without data was a character string "" or there was a comment like "confirmation required". In such a case, the above method was used to extract the number part (including decimals, of course) of the data.

import pandas as pd

#read data
df=pd.read_csv('data.csv')

#extract number
df=df[df['data1'].map(is_float)]

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