How to determine if a string is a number

Method functions for string processing in Python:

str.isnumeric(): True if only contains numbers; otherwise False. Note: This function can only be used for unicode string

str.isdigit(): True if it contains only digits; otherwise False.

str.isalpha(): True if only contains letters; otherwise False.

str.isalnum(): True if only contains letters or numbers; otherwise False.

Example string:

str_1 = "123"

str_2 = "Abc"

str_3 = "123Abc"

Code processing process:

#用isdigit函数判断是否数字
print(str_1.isdigit())
Ture
print(str_2.isdigit())
False
print(str_3.isdigit())
False
#用isalpha判断是否字母
print(str_1.isalpha())    
False
print(str_2.isalpha())
Ture    
print(str_3.isalpha())    
False
#isalnum判断是否数字和字母的组合
print(str_1.isalnum())    
Ture
print(str_2.isalnum())
Ture
print(str_1.isalnum())    
Ture

Note: If the string contains characters other than letters or numbers, such as spaces, It will also return False

Strict analysis: If there are symbols other than numbers or letters (spaces, semicolons, etc.), it will be False
isalnum() must be numbers and letters Mixing
isalpha() is not case sensitive

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