Given a string, write a Python program to find whether a string contains only numbers or not. Let’s see a few methods to solve the above task.

Method #1: Using isdigit() method 

# Python3 code to demonstrate
# how to check whether string contains
# only numbers or not

# Initialising string
ini_string1 = '1234556'
ini_string2 = 'ab123bc'

# printing initial string
print ("Initial Strings : ", ini_string1, ini_string2)

# Using isdigit()
if ini_string1.isdigit():
	print ("String1 contains all numbers")
else:
	print ("String1 doesn't contains all numbers")
	
if ini_string2.isdigit():
	print ("String2 contains all numbers")
else:
	print ("String2 doesn't contains all numbers")

Output: 

Initial Strings :  1234556 ab123bc
String1 contains all numbers
String2 doesn't contains all numbers

Method #2: Using regex 

# Python3 code to demonstrate
# how to check whether string contains
# only numbers or not
import re

# Initialising string
ini_string1 = '1234556'
ini_string2 = 'ab123bc'

# printing initial string
print ("Initial Strings : ", ini_string1, ini_string2)

# Using regex()
if re.match('^[0-9]*$', ini_string1):
	print ("String1 contains all numbers")
else:
	print ("String1 doesn't contains all numbers")
	
if re.match('^[0-9]*$', ini_string2):
	print ("String2 contains all numbers")
else:
	print ("String2 doesn't contains all numbers")

Output: 

Initial Strings :  1234556 ab123bc
String1 contains all numbers
String2 doesn't contains all numbers

Method #3: Using try/exception 

# Python3 code to demonstrate
# how to check whether string contains
# only numbers or not

# Initialising string
ini_string1 = '1234556'
ini_string2 = 'abc123'

# printing initial string
print ("Initial Strings : ", ini_string1, ini_string2)

# Using try / exception:
try:
	num = int(ini_string1)
	print ("String1 contains only digits")
except:
	print ("String1 doesn'tcontains only digits")
	
try:
	num = int(ini_string2)
	print ("String2 contains only digits")
except:
	print ("String2 doesn't contains only digits")
	

Output: 

Initial Strings :  1234556 abc123
String1 contains only digits
String2 doesn't contains only digits