How do we check in Python whether a string contains only numbers?

Python has an in-built function isdigit() which returns true if all characters in a string are digit (between 0-9)

>>> string='9764135408'
>>> string.isdigit()
True
>>> string='091-9764135408'
>>> string.isdigit()
False

You can also use regex expression to check if string contains digits only.

>>> import re
>>> bool(re.match('^[0-9]+$','9764135408'))
True
>>> bool(re.match('^[0-9]+$','091-9764135408'))
False