Python add zeros before number

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

1    →  01
10   →  10
100  →  100

Mateen Ulhaq

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asked Sep 25, 2008 at 18:06

ashchristopherashchristopher

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0

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}"]

Flimm

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answered Sep 25, 2008 at 18:08

9

You can use str.zfill:

print[str[1].zfill[2]]
print[str[10].zfill[2]]
print[str[100].zfill[2]]

prints:

01
10
100

Neuron

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answered Jul 30, 2010 at 11:58

DatageekDatageek

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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.

phoenix

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answered Sep 25, 2008 at 18:43

BerBer

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2

print['{:02}'.format[1]]
print['{:02}'.format[10]]
print['{:02}'.format[100]]

prints:

01
10
100

Neuron

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answered Nov 13, 2013 at 19:30

KresimirKresimir

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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.

Neuron

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answered Nov 28, 2017 at 14:52

Or this:

print '{0:02d}'.format[1]

answered Nov 10, 2010 at 10:03

ajdajd

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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

Neuron

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answered Apr 27, 2012 at 22:02

ZuLuZuLu

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0

Or another solution.

"{:0>2}".format[number]

Kenly

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answered Nov 22, 2015 at 21:01

WinterChillyWinterChilly

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1

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

answered Mar 11, 2020 at 18:50

Nicolas GervaisNicolas Gervais

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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
Type "help", "copyright", "credits" or "license" for more information.
>>> 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
>>> 

answered Jun 21, 2018 at 0:43

RobertoRoberto

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1

width = 5
num = 3
formatted = [width - len[str[num]]] * "0" + str[num]
print formatted

answered Nov 15, 2013 at 16:33

nvdnvd

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Use:

'00'[len[str[i]]:] + str[i]

Or with the math module:

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

answered Apr 20, 2018 at 13:21

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

answered Mar 9, 2021 at 18:51

handlehandle

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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]

answered Oct 2, 2021 at 11:23

You could also do:

'{:0>2}'.format[1]

which will return a string.

answered May 16 at 19:04

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

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

answered Feb 19, 2016 at 4:20

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