Convert list of ints to one number

Question

I have a list of integers that I would like to convert to one number like   numList    1  2  3  num   magic numList   print num  type num   gt  gt  gt  123   lt type  int  gt    What is the best way to implement the magic function   EDIT  I did find this  but it seems like there has to be a better way

User · Answer

Using a generator expression   def magic numbers       digits      join str n  for n in numbers      return int digits

User · Answer

Two solutions    gt  gt  gt  nums    1  2  3   gt  gt  gt  magic   lambda nums  int    join str i  for i in nums     Generator exp   gt  gt  gt  magic nums  123  gt  gt  gt  magic   lambda nums  sum digit   10     len nums  - 1 - i    Summation         for i  digit in enumerate nums    gt  gt  gt  magic nums  123   The map-oriented solution actually comes out ahead on my box -- you definitely should not use sum for things that might be large numbers     import collections import random import timeit  import matplotlib pyplot as pyplot  MICROSECONDS PER SECOND   1E6 FUNS      def test fun fun       FUNS append fun      return fun   test fun def with map nums       return int    join map str  nums      test fun def with interpolation nums       return int    join   d    num for num in nums     test fun def with genexp nums       return int    join str num  for num in nums     test fun def with sum nums       return sum digit   10     len nums  - 1 - i          for i  digit in enumerate nums     test fun def with reduce nums       return int reduce lambda x  y  x   str y   nums         test fun def with builtins nums       return int filter str isdigit  repr nums      test fun def with accumulator nums       tot   0     for num in nums          tot    10         tot    num     return tot  def time test digit count  test count 10000                return  Map from func name to  normalized  microseconds per pass              print  Digit count    digit count     nums    random randrange 1  10  for i in xrange digit count       stmt    to int  r     nums     result by method          for fun in FUNS          setup    from  s import  s as to int       name    fun func name          t   timeit Timer stmt  setup          per pass   t timeit number test count    test count         per pass    MICROSECONDS PER SECOND         print   20s    2f usec pass     fun func name  per pass          result by method fun func name    per pass     return result by method  if   name         main         pass times by method   collections defaultdict list      assert results    fun  1  2  3   for fun in FUNS      assert all result    123 for result in assert results      digit counts   range 1  100  2      for digit count in digit counts          for method  result in time test digit count  iteritems                pass times by method method  append result      for method  pass times in pass times by method iteritems            pyplot plot digit counts  pass times  label method      pyplot legend loc  upper left       pyplot xlabel  Number of Digits       pyplot ylabel  Microseconds       pyplot show

User · Answer

Using a generator expression   def magic numbers       digits      join str n  for n in numbers      return int digits

User · Answer

Just for completeness  here s a variant that uses print    works on Python 2 6-3 x    from   future   import print function try  from cStringIO import StringIO except ImportError       from io import StringIO  def to int nums   s   StringIO         print  nums  sep     end     file  s      s    s getvalue        s truncate 0      return int s    Time performance of different solutions  I ve measured performance of  cdleary s functions  The results are slightly different    Each function tested with the input list generated by   def randrange1 10 digit count     same as  cdleary     return  random randrange 1  10  for i in xrange digit count     You may supply your own function via --sequence-creator yourmodule yourfunction command-line argument  see below    The fastest functions for a given number of integers in a list  len nums     digit count  are    len nums  in 1  30   def  accumulator nums       tot   0     for num in nums          tot    10         tot    num     return tot  len nums  in 30  1000   def  map nums       return int    join map str  nums     def  imap nums       return int    join imap str  nums          ------------------------------ -------------------    Fitting polynom                Function             ------------------------------ -------------------    1 00  log2 N       1 25e-015   N                     2 00  log2 N       5 31e-018   N N                   1 19  log2 N           1 116   N log2 N              1 37  log2 N           2 232   N log2 N  log2 N     ------------------------------ -------------------    1 21  log2 N           0 063    interpolation        1 24  log2 N    -      0 610    genexp               1 25  log2 N    -      0 968    imap                 1 30  log2 N    -      1 917    map                    To plot the first figure download cdleary py and make-figures py and run  numpy and matplotlib must be installed to plot      python cdleary py    Or     python make-figures py --sort-function cdleary  map    gt  --sort-function cdleary  imap    gt  --sort-function cdleary  interpolation    gt  --sort-function cdleary  genexp --sort-function cdleary  sum    gt  --sort-function cdleary  reduce --sort-function cdleary  builtins    gt  --sort-function cdleary  accumulator    gt  --sequence-creator cdleary randrange1 10 --maxn 1000

User · Answer

def magic numbers       return int    join     d  x for x in numbers

User · Answer

This seems pretty clean  to me   def magic  aList  base 10        n  0     for d in aList          n   base n   d     return n

User · Answer

A one-liner without needing to cast to and from str  def magic num       return sum e   10  i for i  e in enumerate num   -1

User · Answer

Using a generator expression   def magic numbers       digits      join str n  for n in numbers      return int digits

User · Answer

pseudo-code   int magic list nums      int tot   0    while   nums isEmpty            int digit   nums takeFirst       tot    10     tot    digit        return tot

User · Answer

Over-explaining a bit  def magic numList              1 2 3      s   map str  numList        1   2   3       s      join s              123      s   int s                 123     return s     How I d probably write it  def magic numList       s      join map str  numList       return int s      As a one-liner   num   int    join map str numList        Functionally  s   reduce lambda x y  x str y   numList      num   int s      Using some oft-forgotten built-ins  s   filter str isdigit  repr numList   num   int s

User · Answer

def magic numbers       return int    join     d  x for x in numbers

User · Answer

def magic numbers       return int    join     d  x for x in numbers

User · Answer

def magic number       return int    join str i  for i in number

User · Answer

I found some examples are not compatible with python 3 I test one from  Triptych  s   filter str isdigit  repr numList   num   int s   in python 3 it s gonna give error  TypeError  int   argument must be a string  a bytes-like object or a number  not  filter   i think the more simple and compatible way would be   def magic num list       return int    join map str  num list

User · Answer

def magic numbers       return int    join     d  x for x in numbers

User · Answer

if the list contains only integer    reduce lambda x y  x 10 y  list

User · Answer

Just for completeness  here s a variant that uses print    works on Python 2 6-3 x    from   future   import print function try  from cStringIO import StringIO except ImportError       from io import StringIO  def to int nums   s   StringIO         print  nums  sep     end     file  s      s    s getvalue        s truncate 0      return int s    Time performance of different solutions  I ve measured performance of  cdleary s functions  The results are slightly different    Each function tested with the input list generated by   def randrange1 10 digit count     same as  cdleary     return  random randrange 1  10  for i in xrange digit count     You may supply your own function via --sequence-creator yourmodule yourfunction command-line argument  see below    The fastest functions for a given number of integers in a list  len nums     digit count  are    len nums  in 1  30   def  accumulator nums       tot   0     for num in nums          tot    10         tot    num     return tot  len nums  in 30  1000   def  map nums       return int    join map str  nums     def  imap nums       return int    join imap str  nums          ------------------------------ -------------------    Fitting polynom                Function             ------------------------------ -------------------    1 00  log2 N       1 25e-015   N                     2 00  log2 N       5 31e-018   N N                   1 19  log2 N           1 116   N log2 N              1 37  log2 N           2 232   N log2 N  log2 N     ------------------------------ -------------------    1 21  log2 N           0 063    interpolation        1 24  log2 N    -      0 610    genexp               1 25  log2 N    -      0 968    imap                 1 30  log2 N    -      1 917    map                    To plot the first figure download cdleary py and make-figures py and run  numpy and matplotlib must be installed to plot      python cdleary py    Or     python make-figures py --sort-function cdleary  map    gt  --sort-function cdleary  imap    gt  --sort-function cdleary  interpolation    gt  --sort-function cdleary  genexp --sort-function cdleary  sum    gt  --sort-function cdleary  reduce --sort-function cdleary  builtins    gt  --sort-function cdleary  accumulator    gt  --sequence-creator cdleary randrange1 10 --maxn 1000

User · Answer

I found this thread while trying to convert a list to the real value of the underlying int in terms of a C-style pointer  but none of the other answers appear to work for this case  I think the following solution works as intended and could be useful to others even though it doesn t necessarily answer the original question   def listToInt x  reverseBytes False     if reverseBytes      x   x   -1    return reduce lambda x y  x 256 y  x    listToInt  1  249      505  listToInt  249  1   True     505  The primary value of this is to emulate the behavior of casting a byte array to another data type  e g  uint16  which Python can t seem to do natively  on either a big or little endian system

User · Answer

Two solutions    gt  gt  gt  nums    1  2  3   gt  gt  gt  magic   lambda nums  int    join str i  for i in nums     Generator exp   gt  gt  gt  magic nums  123  gt  gt  gt  magic   lambda nums  sum digit   10     len nums  - 1 - i    Summation         for i  digit in enumerate nums    gt  gt  gt  magic nums  123   The map-oriented solution actually comes out ahead on my box -- you definitely should not use sum for things that might be large numbers     import collections import random import timeit  import matplotlib pyplot as pyplot  MICROSECONDS PER SECOND   1E6 FUNS      def test fun fun       FUNS append fun      return fun   test fun def with map nums       return int    join map str  nums      test fun def with interpolation nums       return int    join   d    num for num in nums     test fun def with genexp nums       return int    join str num  for num in nums     test fun def with sum nums       return sum digit   10     len nums  - 1 - i          for i  digit in enumerate nums     test fun def with reduce nums       return int reduce lambda x  y  x   str y   nums         test fun def with builtins nums       return int filter str isdigit  repr nums      test fun def with accumulator nums       tot   0     for num in nums          tot    10         tot    num     return tot  def time test digit count  test count 10000                return  Map from func name to  normalized  microseconds per pass              print  Digit count    digit count     nums    random randrange 1  10  for i in xrange digit count       stmt    to int  r     nums     result by method          for fun in FUNS          setup    from  s import  s as to int       name    fun func name          t   timeit Timer stmt  setup          per pass   t timeit number test count    test count         per pass    MICROSECONDS PER SECOND         print   20s    2f usec pass     fun func name  per pass          result by method fun func name    per pass     return result by method  if   name         main         pass times by method   collections defaultdict list      assert results    fun  1  2  3   for fun in FUNS      assert all result    123 for result in assert results      digit counts   range 1  100  2      for digit count in digit counts          for method  result in time test digit count  iteritems                pass times by method method  append result      for method  pass times in pass times by method iteritems            pyplot plot digit counts  pass times  label method      pyplot legend loc  upper left       pyplot xlabel  Number of Digits       pyplot ylabel  Microseconds       pyplot show

User · Answer

This may be helpful  def digits to number digits       return reduce lambda x y   x y  map str digits    print digits to number  1 2 3 4 5

User · Answer

Using a generator expression   def magic numbers       digits      join str n  for n in numbers      return int digits

User · Answer

A one-liner without needing to cast to and from str  def magic num       return sum e   10  i for i  e in enumerate num   -1

User · Answer

I found some examples are not compatible with python 3 I test one from  Triptych  s   filter str isdigit  repr numList   num   int s   in python 3 it s gonna give error  TypeError  int   argument must be a string  a bytes-like object or a number  not  filter   i think the more simple and compatible way would be   def magic num list       return int    join map str  num list

User · Answer

This seems pretty clean  to me   def magic  aList  base 10        n  0     for d in aList          n   base n   d     return n

User · Answer

If you happen to be using numpy  with import numpy as np    In  24   x Out 24   array  1  2  3  4  5    In  25   np dot x  10  np arange len x -1  -1  -1   Out 25   12345

User · Answer

I found this thread while trying to convert a list to the real value of the underlying int in terms of a C-style pointer  but none of the other answers appear to work for this case  I think the following solution works as intended and could be useful to others even though it doesn t necessarily answer the original question   def listToInt x  reverseBytes False     if reverseBytes      x   x   -1    return reduce lambda x y  x 256 y  x    listToInt  1  249      505  listToInt  249  1   True     505  The primary value of this is to emulate the behavior of casting a byte array to another data type  e g  uint16  which Python can t seem to do natively  on either a big or little endian system

User · Answer

This method works in 2 x as long as each element in the list is only a single digit   But you shouldn t actually use this   It s horrible    gt  gt  gt  magic   lambda l int  l  1  3    gt  gt  gt  magic  3 1 3 3 7   31337

User · Answer

Two solutions    gt  gt  gt  nums    1  2  3   gt  gt  gt  magic   lambda nums  int    join str i  for i in nums     Generator exp   gt  gt  gt  magic nums  123  gt  gt  gt  magic   lambda nums  sum digit   10     len nums  - 1 - i    Summation         for i  digit in enumerate nums    gt  gt  gt  magic nums  123   The map-oriented solution actually comes out ahead on my box -- you definitely should not use sum for things that might be large numbers     import collections import random import timeit  import matplotlib pyplot as pyplot  MICROSECONDS PER SECOND   1E6 FUNS      def test fun fun       FUNS append fun      return fun   test fun def with map nums       return int    join map str  nums      test fun def with interpolation nums       return int    join   d    num for num in nums     test fun def with genexp nums       return int    join str num  for num in nums     test fun def with sum nums       return sum digit   10     len nums  - 1 - i          for i  digit in enumerate nums     test fun def with reduce nums       return int reduce lambda x  y  x   str y   nums         test fun def with builtins nums       return int filter str isdigit  repr nums      test fun def with accumulator nums       tot   0     for num in nums          tot    10         tot    num     return tot  def time test digit count  test count 10000                return  Map from func name to  normalized  microseconds per pass              print  Digit count    digit count     nums    random randrange 1  10  for i in xrange digit count       stmt    to int  r     nums     result by method          for fun in FUNS          setup    from  s import  s as to int       name    fun func name          t   timeit Timer stmt  setup          per pass   t timeit number test count    test count         per pass    MICROSECONDS PER SECOND         print   20s    2f usec pass     fun func name  per pass          result by method fun func name    per pass     return result by method  if   name         main         pass times by method   collections defaultdict list      assert results    fun  1  2  3   for fun in FUNS      assert all result    123 for result in assert results      digit counts   range 1  100  2      for digit count in digit counts          for method  result in time test digit count  iteritems                pass times by method method  append result      for method  pass times in pass times by method iteritems            pyplot plot digit counts  pass times  label method      pyplot legend loc  upper left       pyplot xlabel  Number of Digits       pyplot ylabel  Microseconds       pyplot show

User · Answer

Too late for the party here is the approch without converting to string x 0 k len a -1 for i in a      x   10  k  i     k- 1

User · Answer

This method works in 2 x as long as each element in the list is only a single digit   But you shouldn t actually use this   It s horrible    gt  gt  gt  magic   lambda l int  l  1  3    gt  gt  gt  magic  3 1 3 3 7   31337

User · Answer

Over-explaining a bit  def magic numList              1 2 3      s   map str  numList        1   2   3       s      join s              123      s   int s                 123     return s     How I d probably write it  def magic numList       s      join map str  numList       return int s      As a one-liner   num   int    join map str numList        Functionally  s   reduce lambda x y  x str y   numList      num   int s      Using some oft-forgotten built-ins  s   filter str isdigit  repr numList   num   int s

User · Answer

pseudo-code   int magic list nums      int tot   0    while   nums isEmpty            int digit   nums takeFirst       tot    10     tot    digit        return tot

User · Answer

Too late for the party here is the approch without converting to string x 0 k len a -1 for i in a      x   10  k  i     k- 1

User · Answer

def magic number       return int    join str i  for i in number

User · Answer

def magic number       return int    join str i  for i in number

User · Answer

This method works in 2 x as long as each element in the list is only a single digit   But you shouldn t actually use this   It s horrible    gt  gt  gt  magic   lambda l int  l  1  3    gt  gt  gt  magic  3 1 3 3 7   31337

User · Answer

if the list contains only integer    reduce lambda x y  x 10 y  list

User · Answer

Over-explaining a bit  def magic numList              1 2 3      s   map str  numList        1   2   3       s      join s              123      s   int s                 123     return s     How I d probably write it  def magic numList       s      join map str  numList       return int s      As a one-liner   num   int    join map str numList        Functionally  s   reduce lambda x y  x str y   numList      num   int s      Using some oft-forgotten built-ins  s   filter str isdigit  repr numList   num   int s

User · Answer

This may be helpful  def digits to number digits       return reduce lambda x y   x y  map str digits    print digits to number  1 2 3 4 5

User · Answer

pseudo-code   int magic list nums      int tot   0    while   nums isEmpty            int digit   nums takeFirst       tot    10     tot    digit        return tot

User · Answer

If you happen to be using numpy  with import numpy as np    In  24   x Out 24   array  1  2  3  4  5    In  25   np dot x  10  np arange len x -1  -1  -1   Out 25   12345

User · Answer

Over-explaining a bit  def magic numList              1 2 3      s   map str  numList        1   2   3       s      join s              123      s   int s                 123     return s     How I d probably write it  def magic numList       s      join map str  numList       return int s      As a one-liner   num   int    join map str numList        Functionally  s   reduce lambda x y  x str y   numList      num   int s      Using some oft-forgotten built-ins  s   filter str isdigit  repr numList   num   int s

User · Answer

This seems pretty clean  to me   def magic  aList  base 10        n  0     for d in aList          n   base n   d     return n

User · Answer

Just for completeness  here s a variant that uses print    works on Python 2 6-3 x    from   future   import print function try  from cStringIO import StringIO except ImportError       from io import StringIO  def to int nums   s   StringIO         print  nums  sep     end     file  s      s    s getvalue        s truncate 0      return int s    Time performance of different solutions  I ve measured performance of  cdleary s functions  The results are slightly different    Each function tested with the input list generated by   def randrange1 10 digit count     same as  cdleary     return  random randrange 1  10  for i in xrange digit count     You may supply your own function via --sequence-creator yourmodule yourfunction command-line argument  see below    The fastest functions for a given number of integers in a list  len nums     digit count  are    len nums  in 1  30   def  accumulator nums       tot   0     for num in nums          tot    10         tot    num     return tot  len nums  in 30  1000   def  map nums       return int    join map str  nums     def  imap nums       return int    join imap str  nums          ------------------------------ -------------------    Fitting polynom                Function             ------------------------------ -------------------    1 00  log2 N       1 25e-015   N                     2 00  log2 N       5 31e-018   N N                   1 19  log2 N           1 116   N log2 N              1 37  log2 N           2 232   N log2 N  log2 N     ------------------------------ -------------------    1 21  log2 N           0 063    interpolation        1 24  log2 N    -      0 610    genexp               1 25  log2 N    -      0 968    imap                 1 30  log2 N    -      1 917    map                    To plot the first figure download cdleary py and make-figures py and run  numpy and matplotlib must be installed to plot      python cdleary py    Or     python make-figures py --sort-function cdleary  map    gt  --sort-function cdleary  imap    gt  --sort-function cdleary  interpolation    gt  --sort-function cdleary  genexp --sort-function cdleary  sum    gt  --sort-function cdleary  reduce --sort-function cdleary  builtins    gt  --sort-function cdleary  accumulator    gt  --sequence-creator cdleary randrange1 10 --maxn 1000

User · Answer

pseudo-code   int magic list nums      int tot   0    while   nums isEmpty            int digit   nums takeFirst       tot    10     tot    digit        return tot

User · Answer

This method works in 2 x as long as each element in the list is only a single digit   But you shouldn t actually use this   It s horrible    gt  gt  gt  magic   lambda l int  l  1  3    gt  gt  gt  magic  3 1 3 3 7   31337

User · Answer

def magic number       return int    join str i  for i in number

User · Answer

This seems pretty clean  to me   def magic  aList  base 10        n  0     for d in aList          n   base n   d     return n

User · Answer

Two solutions    gt  gt  gt  nums    1  2  3   gt  gt  gt  magic   lambda nums  int    join str i  for i in nums     Generator exp   gt  gt  gt  magic nums  123  gt  gt  gt  magic   lambda nums  sum digit   10     len nums  - 1 - i    Summation         for i  digit in enumerate nums    gt  gt  gt  magic nums  123   The map-oriented solution actually comes out ahead on my box -- you definitely should not use sum for things that might be large numbers     import collections import random import timeit  import matplotlib pyplot as pyplot  MICROSECONDS PER SECOND   1E6 FUNS      def test fun fun       FUNS append fun      return fun   test fun def with map nums       return int    join map str  nums      test fun def with interpolation nums       return int    join   d    num for num in nums     test fun def with genexp nums       return int    join str num  for num in nums     test fun def with sum nums       return sum digit   10     len nums  - 1 - i          for i  digit in enumerate nums     test fun def with reduce nums       return int reduce lambda x  y  x   str y   nums         test fun def with builtins nums       return int filter str isdigit  repr nums      test fun def with accumulator nums       tot   0     for num in nums          tot    10         tot    num     return tot  def time test digit count  test count 10000                return  Map from func name to  normalized  microseconds per pass              print  Digit count    digit count     nums    random randrange 1  10  for i in xrange digit count       stmt    to int  r     nums     result by method          for fun in FUNS          setup    from  s import  s as to int       name    fun func name          t   timeit Timer stmt  setup          per pass   t timeit number test count    test count         per pass    MICROSECONDS PER SECOND         print   20s    2f usec pass     fun func name  per pass          result by method fun func name    per pass     return result by method  if   name         main         pass times by method   collections defaultdict list      assert results    fun  1  2  3   for fun in FUNS      assert all result    123 for result in assert results      digit counts   range 1  100  2      for digit count in digit counts          for method  result in time test digit count  iteritems                pass times by method method  append result      for method  pass times in pass times by method iteritems            pyplot plot digit counts  pass times  label method      pyplot legend loc  upper left       pyplot xlabel  Number of Digits       pyplot ylabel  Microseconds       pyplot show

User · Answer

Just for completeness  here s a variant that uses print    works on Python 2 6-3 x    from   future   import print function try  from cStringIO import StringIO except ImportError       from io import StringIO  def to int nums   s   StringIO         print  nums  sep     end     file  s      s    s getvalue        s truncate 0      return int s    Time performance of different solutions  I ve measured performance of  cdleary s functions  The results are slightly different    Each function tested with the input list generated by   def randrange1 10 digit count     same as  cdleary     return  random randrange 1  10  for i in xrange digit count     You may supply your own function via --sequence-creator yourmodule yourfunction command-line argument  see below    The fastest functions for a given number of integers in a list  len nums     digit count  are    len nums  in 1  30   def  accumulator nums       tot   0     for num in nums          tot    10         tot    num     return tot  len nums  in 30  1000   def  map nums       return int    join map str  nums     def  imap nums       return int    join imap str  nums          ------------------------------ -------------------    Fitting polynom                Function             ------------------------------ -------------------    1 00  log2 N       1 25e-015   N                     2 00  log2 N       5 31e-018   N N                   1 19  log2 N           1 116   N log2 N              1 37  log2 N           2 232   N log2 N  log2 N     ------------------------------ -------------------    1 21  log2 N           0 063    interpolation        1 24  log2 N    -      0 610    genexp               1 25  log2 N    -      0 968    imap                 1 30  log2 N    -      1 917    map                    To plot the first figure download cdleary py and make-figures py and run  numpy and matplotlib must be installed to plot      python cdleary py    Or     python make-figures py --sort-function cdleary  map    gt  --sort-function cdleary  imap    gt  --sort-function cdleary  interpolation    gt  --sort-function cdleary  genexp --sort-function cdleary  sum    gt  --sort-function cdleary  reduce --sort-function cdleary  builtins    gt  --sort-function cdleary  accumulator    gt  --sequence-creator cdleary randrange1 10 --maxn 1000

[python] Convert list of ints to one number?

Examples related to python