In Python 2 (and Python 3) you can do:
number = 1
print("%02d" % (number,))
Basically % is like printf or sprintf (see docs).
For Python 3.+, the same behavior can also be achieved with format:
number = 1
print("{:02d}".format(number))
For Python 3.6+ the same behavior can be achieved with f-strings:
number = 1
print(f"{number:02d}")