# Display number with leading zeros

## Question:

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

``````1    →  01
10   →  10
100  →  100
``````

``````x = [1, 10, 100]
for i in x:
print '%02d' % i
``````

results in:

``````01
10
100
``````

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}")
``````

Use a format string – http://docs.python.org/lib/typesseq-strings.html

For example:

``````python -c 'print "%(num)02d" % {"num":5}'
``````

In Python 2.6+ and 3.0+, you would use the `format()` string method:

``````for i in (1, 10, 100):
print('{num:02d}'.format(num=i))
``````

or using the built-in (for a single number):

``````print(format(i, '02d'))
``````

See the PEP-3101 documentation for the new formatting functions.

You can use `str.zfill`:

``````print(str(1).zfill(2))
print(str(10).zfill(2))
print(str(100).zfill(2))
``````

prints:

``````01
10
100
``````

Or this:

`print '{0:02d}'.format(1)`

The Pythonic way to do this:

``````str(number).rjust(string_width, fill_char)
``````

This way, the original string is returned unchanged if its length is greater than string_width. Example:

``````a = [1, 10, 100]
for num in a:
print str(num).rjust(2, '0')
``````

Results:

``````01
10
100
``````
``````print('{:02}'.format(1))
print('{:02}'.format(10))
print('{:02}'.format(100))
``````

prints:

``````01
10
100
``````
``````width = 5
num = 3
formatted = (width - len(str(num))) * "0" + str(num)
print formatted
``````

Or another solution.

``````"{:0>2}".format(number)
``````

If dealing with numbers that are either one or two digits:

`'0'+str(number)[-2:]` or `'0{0}'.format(number)[-2:]`

In Python >= 3.6, you can do this succinctly with the new f-strings that were introduced by using:

``````f'{val:02}'
``````

which prints the variable with name `val` with a `fill` value of `0` and a `width` of `2`.

For your specific example you can do this nicely in a loop:

``````a, b, c = 1, 10, 100
for val in [a, b, c]:
print(f'{val:02}')
``````

which prints:

``````01
10
100
``````

For more information on f-strings, take a look at PEP 498 where they were introduced.

Use:

``````'00'[len(str(i)):] + str(i)
``````

Or with the `math` module:

``````import math
'00'[math.ceil(math.log(i, 10)):] + str(i)
``````

This is how I do it:

``````str(1).zfill(len(str(total)))
``````

Basically zfill takes the number of leading zeros you want to add, so it’s easy to take the biggest number, turn it into a string and get the length, like this:

```Python 3.6.5 (default, May 11 2018, 04:00:52)
[GCC 8.1.0] on linux
>>> total = 100
>>> print(str(1).zfill(len(str(total))))
001
>>> total = 1000
>>> print(str(1).zfill(len(str(total))))
0001
>>> total = 10000
>>> print(str(1).zfill(len(str(total))))
00001
>>>
```

You can do this with f strings.

``````import numpy as np

print(f'{np.random.choice([1, 124, 13566]):0>8}')
``````

This will print constant length of 8, and pad the rest with leading `0`.

``````00000001
00000124
00013566
``````

All of these create the string "01":

``````>python -m timeit "'{:02d}'.format(1)"
1000000 loops, best of 5: 357 nsec per loop

>python -m timeit "'{0:0{1}d}'.format(1,2)"
500000 loops, best of 5: 607 nsec per loop

>python -m timeit "f'{1:02d}'"
1000000 loops, best of 5: 281 nsec per loop

>python -m timeit "f'{1:0{2}d}'"
500000 loops, best of 5: 423 nsec per loop

>python -m timeit "str(1).zfill(2)"
1000000 loops, best of 5: 271 nsec per loop

>python
Python 3.8.1 (tags/v3.8.1:1b293b6, Dec 18 2019, 23:11:46) [MSC v.1916 64 bit (AMD64)] on win32
``````

This would be the Python way, although I would include the parameter for clarity – "{0:0>2}".format(number), if someone will wants nLeadingZeros they should note they can also do:"{0:0>{1}}".format(number, nLeadingZeros + 1)

You could also do:

``````'{:0>2}'.format(1)
``````

which will return a string.

Categories: questions
Answers are sorted by their score. The answer accepted by the question owner as the best is marked with
at the top-right corner.