Python determines whether a string is a pure numeric code

Source: Internet
Author: User

Judged by the code below, through the anomaly can not distinguish between the positive and negative signs, regular expressions can be more flexible according to their needs to write, through the IsDigit method to determine whether it is pure numbers, test code as follows

The code is as follows Copy Code


A = "1"
b = "1.2"
c = "a"
def is_num_by_except (num):
int (num)
Return True
Except ValueError:
# print '%s valueerror '% num
Return False

Print "by throwing an exception"
Print "A", is_num_by_except (a)
Print "B", is_num_by_except (b)
Print "C", Is_num_by_except (c)

Print "Through IsDigit ()"
Print "A", A.isdigit ()
Print "B", B.isdigit ()
Print "C", C.isdigit ()

Print "Through regular expressions"
Import re
Print "A", Re.match (R "d+$", a) and True or False
Print "B", Re.match (R "d+$", b) and True or False
Print "C", Re.match (R "d+$", c) and True or False
The output results are as follows:

By throwing an exception
A True
b False
C False
Through IsDigit ()
A True
b False
C False
Through regular expressions
A True
b False
C False

To determine that a string contains only numeric characters

A: One method is A.isdigit (). However, this method is not valid for numeric strings that contain positive and negative numbers, so it is more accurate:

The code is as follows Copy Code

x = Int (apossibleint)
... do something with x ...
Except ValueError:
... do something else ...

This is more accurate and more adaptable. But if you are convinced that there is no sign, it is more convenient to use the IsDigit () method of the string.

You can also use regular expressions:

The code is as follows Copy Code

Re.match (R ' [+-]?d+$ ', ' -1234′ ')

When the number is large, it may be faster than converting with type int.

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