Best way to format integer as string with leading zeros

Question

I need to add leading zeros to integer to make a string with defined quantity of digits   cnt   What the best way to translate this simple function from PHP to Python   function add nulls  int   cnt 2         int   intval  int       for  i 0   i lt   cnt-strlen  int     i             nulls     0       return  nulls  int      Is there a function that can do this

User · Answer

This is my Python function   def add nulls num  cnt 2     cnt   cnt - len str num     nulls    0    cnt   return   s s     nulls  num

User · Answer

You most likely just need to format your integer     0 d     fill  your int    For example    gt  gt  gt    0 d     3  4   004

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A straightforward conversion would be  again with a function    def add nulls2 int  cnt       nulls   str int      for i in range cnt - len str int             nulls    0    nulls     return nulls

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The standard way is to use format string modifiers  These format string methods are available in most programming languages  via the sprintf function in c for example  and are a handy tool to know about   To output a string of length 5       in Python 3 5 and above   i   random randint 0  99999  print f  i 05d          Python 2 6 and above   print   0 05d   format i        before Python 2 6   print   05d    i   See  https   docs python org 3 library string html

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Python 3 6 f-strings allows us to add leading zeros easily   number   5 print f  now we have leading zeros in  number 02d      Have a look at this good post about this feature

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One-liner alternative to the built-in zfill  This function takes x and converts it to a string  and adds zeros in the beginning only and only if the length is too short  def zfill alternative x len 4   return      0  len  str x   -l   if len str x   lt len else str x     To sum it up - build-in  zfill is good enough  but if someone is curious on how to implement this by hand  here is one more example

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You have at least two options    str zfill  lambda n  cnt 2  str n  zfill cnt    formatting  lambda n  cnt 2    0 d     cnt  n    If on Python  2 5  see a third option in clorz s answer

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For Python 3 and beyond  str zfill   is still the most readable option  But it is a good idea to look into the new and powerful str format    what if you want to pad something that is not 0         if we want to pad 22 with zeros in front  to be 5 digits in length      str output      0 gt 5   format 22      print str output         gt  gt  gt  00022         0 gt 5  meaning    0  means  pad with 0    gt   means move 22 to right most   5  means the total length is 5        another example for comparision     str output        lt 4   format 11      print str output         gt  gt  gt  11          to put it in a less hard-coded format      int inputArg   22     int desiredLength   5     str output     str 0 0 gt  str 1    format str 0 int inputArg  str 1 int desiredLength      print str output         gt  gt  gt  00022

User · Answer

You can use the zfill   method to pad a string with zeros   In  3   str 1  zfill 2  Out 3    01

User · Answer

Python 2 6 allows this   add nulls   lambda number  zero count     0 0 1 d   format number  zero count    gt  gt  gt add nulls 2 3   002

[python] Best way to format integer as string with leading zeros?

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