[ Python 常見問題 ] Display number with leading zeros

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Question 
Given: 

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1. a = 1  
2. b = 10  
3. c = 100  

How do I display a leading zero for all numbers with less than two digits? That is, 

01 
10 
100

How-To 
One approach is to use Format feature from string class: 

>>> print("{:02d}".format(1)) # Filler as '0'; width=2 
01 
>>> print("{:03d}".format(1)) 
001 
>>> print("{:03d}".format(123)) 
123

Or you can use str.zfill: 

>>> print("1".zfill(3)) # Return the numeric string left filled with zeros in a string of length 3 
001 
>>> print("12".zfill(3)) 
012 
>>> print("123".zfill(3)) 
123