How to pad zeroes to a string

Question

What is a Pythonic way to pad a numeric string with zeroes to the left  i e  so the numeric string has a specific length

User · Answer

I am adding how to use a int from a length of a string within an f-string because it didn t appear to be covered   gt  gt  gt  pad number   len  quot this string quot   11  gt  gt  gt  s   f quot  1 0 pad number   quot     gt  gt  gt  s  00000000001

User · Answer

Just use the rjust method of the string object  This example will make a string of 10 characters long  padding as necessary   gt  gt  gt  t    test   gt  gt  gt  t rjust 10   0    gt  gt  gt   000000test

User · Answer

width   10 x   5 print   0 d     width  x   gt  0000000005   See the print documentation for all the exciting details   Update for Python 3 x  7 5 years later   That last line should now be   print   0 d     width  x     I e  print   is now a function  not a statement  Note that I still prefer the Old School printf   style because  IMNSHO  it reads better  and because  um  I ve been using that notation since January  1980  Something     old dogs    something something     new tricks

User · Answer

str n  zfill width  will work with strings  ints  floats    and is Python 2 x and 3 x compatible    gt  gt  gt  n   3  gt  gt  gt  str n  zfill 5   00003   gt  gt  gt  n    3   gt  gt  gt  str n  zfill 5   00003   gt  gt  gt  n    3 0   gt  gt  gt  str n  zfill 5   003 0

User · Answer

For the ones who came here to understand and not just a quick answer  I do these especially for time strings   hour   4 minute   3    0 gt 2    0 gt 2   format hour minute    prints 04 03     0 gt 3    0 gt 5   format hour minute    prints  004 00003      0 lt 3    0 lt 5   format hour minute    prints  400 30000        lt 3      lt 5   format hour minute    prints  4   3            0  symbols what to replace with the  2  padding characters  the default is an empty space          symbols allign all the 2  0  character to the left of the string          symbols the format spec

User · Answer

Another approach would be to use a list comprehension with a condition checking for lengths  Below is a demonstration     input list of strings that we want to prepend zeros In  71   list of str     101010    10101010    11110    0000      prepend zeros to make each string to length 8  if length of string is less than 8 In  83     0   8-len s     s if len s   lt  desired len else s for s in list of str  Out 83     00101010    10101010    00011110    00000000

User · Answer

Strings   gt  gt  gt  n    4   gt  gt  gt  print n zfill 3   004  And for numbers   gt  gt  gt  n   4  gt  gt  gt  print f  n 03      Preferred method  python  gt   3 6 004  gt  gt  gt  print   03d    n  004  gt  gt  gt  print format n   03      python  gt   2 6 004  gt  gt  gt  print   0 03d   format n      python  gt   2 6   python 3 004  gt  gt  gt  print   foo 03d   format foo n      python  gt   2 6   python 3 004  gt  gt  gt  print    03d   format n      python  gt   2 7   python3 004  String formatting documentation

User · Answer

You could also repeat  0   prepend it to str n  and get the rightmost width slice  Quick and dirty little expression   def pad left n  width  pad  0        return   pad   width    str n   -width

User · Answer

For the ones who came here to understand and not just a quick answer  I do these especially for time strings   hour   4 minute   3    0 gt 2    0 gt 2   format hour minute    prints 04 03     0 gt 3    0 gt 5   format hour minute    prints  004 00003      0 lt 3    0 lt 5   format hour minute    prints  400 30000        lt 3      lt 5   format hour minute    prints  4   3            0  symbols what to replace with the  2  padding characters  the default is an empty space          symbols allign all the 2  0  character to the left of the string          symbols the format spec

User · Answer

Besides zfill  you can use general string formatting   print f  number 05d       since Python 3 6   or print    05d   format number     or print   0 05d   format number     or  explicit 0th positional arg  selection  print   n 05d   format n number     or  explicit  n  keyword arg  selection  print format number   05d      Documentation for string formatting and f-strings

User · Answer

str n  zfill width  will work with strings  ints  floats    and is Python 2 x and 3 x compatible    gt  gt  gt  n   3  gt  gt  gt  str n  zfill 5   00003   gt  gt  gt  n    3   gt  gt  gt  str n  zfill 5   00003   gt  gt  gt  n    3 0   gt  gt  gt  str n  zfill 5   003 0

User · Answer

Strings   gt  gt  gt  n    4   gt  gt  gt  print n zfill 3   004  And for numbers   gt  gt  gt  n   4  gt  gt  gt  print f  n 03      Preferred method  python  gt   3 6 004  gt  gt  gt  print   03d    n  004  gt  gt  gt  print format n   03      python  gt   2 6 004  gt  gt  gt  print   0 03d   format n      python  gt   2 6   python 3 004  gt  gt  gt  print   foo 03d   format foo n      python  gt   2 6   python 3 004  gt  gt  gt  print    03d   format n      python  gt   2 7   python3 004  String formatting documentation

User · Answer

gt  gt  gt   99  zfill 5   00099   gt  gt  gt   99  rjust 5  0    00099    if you want the opposite    gt  gt  gt   99  ljust 5  0    99000

User · Answer

For zip codes saved as integers    gt  gt  gt  a   6340  gt  gt  gt  b   90210  gt  gt  gt  print   05d    a 06340  gt  gt  gt  print   05d    b 90210

User · Answer

For Python 3 6  using f-strings    gt  gt  gt  i   1  gt  gt  gt  f  i 0 gt 2      Works for both numbers and strings   01   gt  gt  gt  f  i 02      Works only for numbers   01    For Python 2 to Python 3 5    gt  gt  gt     0 gt 2   format  1      Works for both numbers and strings   01   gt  gt  gt     02   format 1     Works only for numbers   01

User · Answer

I am adding how to use a int from a length of a string within an f-string because it didn t appear to be covered   gt  gt  gt  pad number   len  quot this string quot   11  gt  gt  gt  s   f quot  1 0 pad number   quot     gt  gt  gt  s  00000000001

User · Answer

Just use the rjust method of the string object  This example will make a string of 10 characters long  padding as necessary   gt  gt  gt  t    test   gt  gt  gt  t rjust 10   0    gt  gt  gt   000000test

User · Answer

For Python 3 6  using f-strings    gt  gt  gt  i   1  gt  gt  gt  f  i 0 gt 2      Works for both numbers and strings   01   gt  gt  gt  f  i 02      Works only for numbers   01    For Python 2 to Python 3 5    gt  gt  gt     0 gt 2   format  1      Works for both numbers and strings   01   gt  gt  gt     02   format 1     Works only for numbers   01

User · Answer

I made a function   def PadNumber number  n pad  add prefix None       number str   str number      paded number   number str zfill n pad      if add prefix          paded number   add prefix paded number     print paded number   PadNumber 99  4  PadNumber 1011  8   quot b  quot   PadNumber  7BEF   6   quot   quot    The output   0099 b 00001011  007BEF

User · Answer

When using Python  gt   3 6  the cleanest way is to use f-strings with string formatting    gt  gt  gt  s   f  1 08      inline with int  gt  gt  gt  s  00000001       gt  gt  gt  s   f   1  0 gt 8      inline with str  gt  gt  gt  s  00000001       gt  gt  gt  n   1  gt  gt  gt  s   f  n 08      int variable  gt  gt  gt  s  00000001       gt  gt  gt  c    1   gt  gt  gt  s   f  c 0 gt 8      str variable  gt  gt  gt  s  00000001    I would prefer formatting with an int  since only then the sign is handled correctly    gt  gt  gt  f  -1 08    -0000001    gt  gt  gt  f  1  08     0000001    gt  gt  gt  f   -1  0 gt 8    000000-1

User · Answer

Strings   gt  gt  gt  n    4   gt  gt  gt  print n zfill 3   004  And for numbers   gt  gt  gt  n   4  gt  gt  gt  print f  n 03      Preferred method  python  gt   3 6 004  gt  gt  gt  print   03d    n  004  gt  gt  gt  print format n   03      python  gt   2 6 004  gt  gt  gt  print   0 03d   format n      python  gt   2 6   python 3 004  gt  gt  gt  print   foo 03d   format foo n      python  gt   2 6   python 3 004  gt  gt  gt  print    03d   format n      python  gt   2 7   python3 004  String formatting documentation

User · Answer

Its ok too    h   2  m   7  s   3  print   02d  02d  02d     h  m  s     so output will be   02 07 03

User · Answer

Quick timing comparison   setup       from random import randint def test 1        num   randint 0 1000000      return str num  zfill 7  def test 2        num   randint 0 1000000      return format num   07   def test 3        num   randint 0 1000000      return   0 07d   format num  def test 4        num   randint 0 1000000      return format num   07d   def test 5        num   randint 0 1000000      return    07d   format num  def test 6        num   randint 0 1000000      return   x 07d   format x num  def test 7        num   randint 0 1000000      return str num  rjust 7   0       import timeit print timeit Timer  test 1     setup setup  repeat 3  900000  print timeit Timer  test 2     setup setup  repeat 3  900000  print timeit Timer  test 3     setup setup  repeat 3  900000  print timeit Timer  test 4     setup setup  repeat 3  900000  print timeit Timer  test 5     setup setup  repeat 3  900000  print timeit Timer  test 6     setup setup  repeat 3  900000  print timeit Timer  test 7     setup setup  repeat 3  900000     gt   2 281613943830961  2 2719342631547077  2 261691106209631   gt   2 311480238815406  2 318420542148333  2 3552384305184493   gt   2 3824197456864304  2 3457239951596485  2 3353268829498646   gt   2 312442972404032  2 318053102249902  2 3054072168069872   gt   2 3482314132374853  2 3403386400002475  2 330108825844775   gt   2 424549090688892  2 4346475296851438  2 429691196530058   gt   2 3259756401716487  2 333549212826732  2 32049893822186    I ve made different tests of different repetitions  The differences are not huge  but in all tests  the zfill solution was fastest

User · Answer

You could also repeat  0   prepend it to str n  and get the rightmost width slice  Quick and dirty little expression   def pad left n  width  pad  0        return   pad   width    str n   -width

User · Answer

What is the most pythonic way to pad a numeric string with zeroes to the left  i e   so the numeric string has a specific length    str zfill is specifically intended to do this    gt  gt  gt   1  zfill 4   0001    Note that it is specifically intended to handle numeric strings as requested  and moves a   or - to the beginning of the string    gt  gt  gt    1  zfill 4    001   gt  gt  gt   -1  zfill 4   -001    Here s the help on str zfill    gt  gt  gt  help str zfill  Help on method descriptor   zfill          S zfill width  - gt  str      Pad a numeric string S with zeros on the left  to fill a field     of the specified width  The string S is never truncated    Performance  This is also the most performant of alternative methods    gt  gt  gt  min timeit repeat lambda   1  zfill 4    0 18824880896136165  gt  gt  gt  min timeit repeat lambda   1  rjust 4   0     0 2104538488201797  gt  gt  gt  min timeit repeat lambda  f  1 04     0 32585487607866526  gt  gt  gt  min timeit repeat lambda     04   format 1    0 34988890308886766   To best compare apples to apples for the   method  note it is actually slower   which will otherwise pre-calculate    gt  gt  gt  min timeit repeat lambda   1  zfill 0 or 4    0 19728074967861176  gt  gt  gt  min timeit repeat lambda    04d     0 or 1    0 2347015216946602   Implementation  With a little digging  I found the implementation of the zfill method in Objects stringlib transmogrify h   static PyObject   stringlib zfill PyObject  self  PyObject  args        Py ssize t fill      PyObject  s      char  p      Py ssize t width       if   PyArg ParseTuple args   n zfill    amp width           return NULL       if  STRINGLIB LEN self   gt   width            return return self self              fill   width - STRINGLIB LEN self        s   pad self  fill  0   0         if  s    NULL          return NULL       p   STRINGLIB STR s       if  p fill            p fill      -                move sign to beginning of string            p 0    p fill           p fill     0              return s      Let s walk through this C code   It first parses the argument positionally  meaning it doesn t allow keyword arguments     gt  gt  gt   1  zfill width 4  Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt  TypeError  zfill   takes no keyword arguments   It then checks if it s the same length or longer  in which case it returns the string    gt  gt  gt   1  zfill 0   1    zfill calls pad  this pad function is also called by ljust  rjust  and center as well   This basically copies the contents into a new string and fills in the padding   static inline PyObject   pad PyObject  self  Py ssize t left  Py ssize t right  char fill        PyObject  u       if  left  lt  0          left   0      if  right  lt  0          right   0       if  left    0  amp  amp  right    0            return return self self              u   STRINGLIB NEW NULL  left   STRINGLIB LEN self    right       if  u            if  left              memset STRINGLIB STR u   fill  left           memcpy STRINGLIB STR u    left                 STRINGLIB STR self                  STRINGLIB LEN self            if  right              memset STRINGLIB STR u    left   STRINGLIB LEN self                      fill  right              return u      After calling pad  zfill moves any originally preceding   or - to the beginning of the string    Note that for the original string to actually be numeric is not required    gt  gt  gt    foo  zfill 10    000000foo   gt  gt  gt   -foo  zfill 10   -000000foo

User · Answer

width   10 x   5 print   0 d     width  x   gt  0000000005   See the print documentation for all the exciting details   Update for Python 3 x  7 5 years later   That last line should now be   print   0 d     width  x     I e  print   is now a function  not a statement  Note that I still prefer the Old School printf   style because  IMNSHO  it reads better  and because  um  I ve been using that notation since January  1980  Something     old dogs    something something     new tricks

User · Answer

Besides zfill  you can use general string formatting   print f  number 05d       since Python 3 6   or print    05d   format number     or print   0 05d   format number     or  explicit 0th positional arg  selection  print   n 05d   format n number     or  explicit  n  keyword arg  selection  print format number   05d      Documentation for string formatting and f-strings

User · Answer

Besides zfill  you can use general string formatting   print f  number 05d       since Python 3 6   or print    05d   format number     or print   0 05d   format number     or  explicit 0th positional arg  selection  print   n 05d   format n number     or  explicit  n  keyword arg  selection  print format number   05d      Documentation for string formatting and f-strings

User · Answer

Besides zfill  you can use general string formatting   print f  number 05d       since Python 3 6   or print    05d   format number     or print   0 05d   format number     or  explicit 0th positional arg  selection  print   n 05d   format n number     or  explicit  n  keyword arg  selection  print format number   05d      Documentation for string formatting and f-strings

User · Answer

gt  gt  gt   99  zfill 5   00099   gt  gt  gt   99  rjust 5  0    00099    if you want the opposite    gt  gt  gt   99  ljust 5  0    99000

User · Answer

What is the most pythonic way to pad a numeric string with zeroes to the left  i e   so the numeric string has a specific length    str zfill is specifically intended to do this    gt  gt  gt   1  zfill 4   0001    Note that it is specifically intended to handle numeric strings as requested  and moves a   or - to the beginning of the string    gt  gt  gt    1  zfill 4    001   gt  gt  gt   -1  zfill 4   -001    Here s the help on str zfill    gt  gt  gt  help str zfill  Help on method descriptor   zfill          S zfill width  - gt  str      Pad a numeric string S with zeros on the left  to fill a field     of the specified width  The string S is never truncated    Performance  This is also the most performant of alternative methods    gt  gt  gt  min timeit repeat lambda   1  zfill 4    0 18824880896136165  gt  gt  gt  min timeit repeat lambda   1  rjust 4   0     0 2104538488201797  gt  gt  gt  min timeit repeat lambda  f  1 04     0 32585487607866526  gt  gt  gt  min timeit repeat lambda     04   format 1    0 34988890308886766   To best compare apples to apples for the   method  note it is actually slower   which will otherwise pre-calculate    gt  gt  gt  min timeit repeat lambda   1  zfill 0 or 4    0 19728074967861176  gt  gt  gt  min timeit repeat lambda    04d     0 or 1    0 2347015216946602   Implementation  With a little digging  I found the implementation of the zfill method in Objects stringlib transmogrify h   static PyObject   stringlib zfill PyObject  self  PyObject  args        Py ssize t fill      PyObject  s      char  p      Py ssize t width       if   PyArg ParseTuple args   n zfill    amp width           return NULL       if  STRINGLIB LEN self   gt   width            return return self self              fill   width - STRINGLIB LEN self        s   pad self  fill  0   0         if  s    NULL          return NULL       p   STRINGLIB STR s       if  p fill            p fill      -                move sign to beginning of string            p 0    p fill           p fill     0              return s      Let s walk through this C code   It first parses the argument positionally  meaning it doesn t allow keyword arguments     gt  gt  gt   1  zfill width 4  Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt  TypeError  zfill   takes no keyword arguments   It then checks if it s the same length or longer  in which case it returns the string    gt  gt  gt   1  zfill 0   1    zfill calls pad  this pad function is also called by ljust  rjust  and center as well   This basically copies the contents into a new string and fills in the padding   static inline PyObject   pad PyObject  self  Py ssize t left  Py ssize t right  char fill        PyObject  u       if  left  lt  0          left   0      if  right  lt  0          right   0       if  left    0  amp  amp  right    0            return return self self              u   STRINGLIB NEW NULL  left   STRINGLIB LEN self    right       if  u            if  left              memset STRINGLIB STR u   fill  left           memcpy STRINGLIB STR u    left                 STRINGLIB STR self                  STRINGLIB LEN self            if  right              memset STRINGLIB STR u    left   STRINGLIB LEN self                      fill  right              return u      After calling pad  zfill moves any originally preceding   or - to the beginning of the string    Note that for the original string to actually be numeric is not required    gt  gt  gt    foo  zfill 10    000000foo   gt  gt  gt   -foo  zfill 10   -000000foo

User · Answer

Quick timing comparison   setup       from random import randint def test 1        num   randint 0 1000000      return str num  zfill 7  def test 2        num   randint 0 1000000      return format num   07   def test 3        num   randint 0 1000000      return   0 07d   format num  def test 4        num   randint 0 1000000      return format num   07d   def test 5        num   randint 0 1000000      return    07d   format num  def test 6        num   randint 0 1000000      return   x 07d   format x num  def test 7        num   randint 0 1000000      return str num  rjust 7   0       import timeit print timeit Timer  test 1     setup setup  repeat 3  900000  print timeit Timer  test 2     setup setup  repeat 3  900000  print timeit Timer  test 3     setup setup  repeat 3  900000  print timeit Timer  test 4     setup setup  repeat 3  900000  print timeit Timer  test 5     setup setup  repeat 3  900000  print timeit Timer  test 6     setup setup  repeat 3  900000  print timeit Timer  test 7     setup setup  repeat 3  900000     gt   2 281613943830961  2 2719342631547077  2 261691106209631   gt   2 311480238815406  2 318420542148333  2 3552384305184493   gt   2 3824197456864304  2 3457239951596485  2 3353268829498646   gt   2 312442972404032  2 318053102249902  2 3054072168069872   gt   2 3482314132374853  2 3403386400002475  2 330108825844775   gt   2 424549090688892  2 4346475296851438  2 429691196530058   gt   2 3259756401716487  2 333549212826732  2 32049893822186    I ve made different tests of different repetitions  The differences are not huge  but in all tests  the zfill solution was fastest

User · Answer

When using Python  gt   3 6  the cleanest way is to use f-strings with string formatting    gt  gt  gt  s   f  1 08      inline with int  gt  gt  gt  s  00000001       gt  gt  gt  s   f   1  0 gt 8      inline with str  gt  gt  gt  s  00000001       gt  gt  gt  n   1  gt  gt  gt  s   f  n 08      int variable  gt  gt  gt  s  00000001       gt  gt  gt  c    1   gt  gt  gt  s   f  c 0 gt 8      str variable  gt  gt  gt  s  00000001    I would prefer formatting with an int  since only then the sign is handled correctly    gt  gt  gt  f  -1 08    -0000001    gt  gt  gt  f  1  08     0000001    gt  gt  gt  f   -1  0 gt 8    000000-1

User · Answer

width   10 x   5 print   0 d     width  x   gt  0000000005   See the print documentation for all the exciting details   Update for Python 3 x  7 5 years later   That last line should now be   print   0 d     width  x     I e  print   is now a function  not a statement  Note that I still prefer the Old School printf   style because  IMNSHO  it reads better  and because  um  I ve been using that notation since January  1980  Something     old dogs    something something     new tricks

User · Answer

I made a function   def PadNumber number  n pad  add prefix None       number str   str number      paded number   number str zfill n pad      if add prefix          paded number   add prefix paded number     print paded number   PadNumber 99  4  PadNumber 1011  8   quot b  quot   PadNumber  7BEF   6   quot   quot    The output   0099 b 00001011  007BEF

User · Answer

For zip codes saved as integers    gt  gt  gt  a   6340  gt  gt  gt  b   90210  gt  gt  gt  print   05d    a 06340  gt  gt  gt  print   05d    b 90210

User · Answer

Strings   gt  gt  gt  n    4   gt  gt  gt  print n zfill 3   004  And for numbers   gt  gt  gt  n   4  gt  gt  gt  print f  n 03      Preferred method  python  gt   3 6 004  gt  gt  gt  print   03d    n  004  gt  gt  gt  print format n   03      python  gt   2 6 004  gt  gt  gt  print   0 03d   format n      python  gt   2 6   python 3 004  gt  gt  gt  print   foo 03d   format foo n      python  gt   2 6   python 3 004  gt  gt  gt  print    03d   format n      python  gt   2 7   python3 004  String formatting documentation

User · Answer

Another approach would be to use a list comprehension with a condition checking for lengths  Below is a demonstration     input list of strings that we want to prepend zeros In  71   list of str     101010    10101010    11110    0000      prepend zeros to make each string to length 8  if length of string is less than 8 In  83     0   8-len s     s if len s   lt  desired len else s for s in list of str  Out 83     00101010    10101010    00011110    00000000

User · Answer

Just use the rjust method of the string object  This example will make a string of 10 characters long  padding as necessary   gt  gt  gt  t    test   gt  gt  gt  t rjust 10   0    gt  gt  gt   000000test

User · Answer

Its ok too    h   2  m   7  s   3  print   02d  02d  02d     h  m  s     so output will be   02 07 03

User · Answer

Just use the rjust method of the string object  This example will make a string of 10 characters long  padding as necessary   gt  gt  gt  t    test   gt  gt  gt  t rjust 10   0    gt  gt  gt   000000test

User · Answer

width   10 x   5 print   0 d     width  x   gt  0000000005   See the print documentation for all the exciting details   Update for Python 3 x  7 5 years later   That last line should now be   print   0 d     width  x     I e  print   is now a function  not a statement  Note that I still prefer the Old School printf   style because  IMNSHO  it reads better  and because  um  I ve been using that notation since January  1980  Something     old dogs    something something     new tricks

[python] How to pad zeroes to a string?

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