Python's zfill() string method is useful to fill a string with zeros.
Alternatively you could also use an f-string:
>>> for number in range(1, 11):
... str(number).zfill(3)
...
'001'
'002'
'003'
'004'
'005'
'006'
'007'
'008'
'009'
'010'
>>> for number in range(1, 11):
... f"{number:0>3}"
...
'001'
'002'
'003'
'004'
'005'
'006'
'007'
'008'
'009'
'010'
#strings #f-strings