How can I multiply all items in a list together with Python

Question

I need to write a function that takes a list of numbers and multiplies them together  Example   1 2 3 4 5 6  will give me 1 2 3 4 5 6  I could really use your help

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Starting Python 3 8  a  prod function has been included to the math module in the standard library      math prod iterable     start 1    The method returns the product of a start value  default  1  times an iterable of numbers   import math math prod  1  2  3  4  5  6     gt  gt  gt  720   If the iterable is empty  this will produce 1  or the start value  if provided

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I would use the numpy prod to perform the task  See below   import numpy as np mylist    1  2  3  4  5  6   result   np prod np array mylist

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I personally like this for a function that multiplies all elements of a generic list together   def multiply n       total   1     for i in range 0  len n            total    n i      print total   It s compact  uses simple things  a variable and a for loop   and feels intuitive to me  it looks like how I d think of the problem  just take one  multiply it  then multiply by the next  and so on

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My solution   def multiply numbers       a   1     for num in numbers          a    num         return a    pass

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Found this question today but I noticed that it does not have the case where there are None s in the list  So  the complete solution would be   from functools import reduce  a    None  1  2  3  None  4  print reduce lambda x  y   x if x else 1     y if y else 1   a     In the case of addition  we have    print reduce lambda x  y   x if x else 0     y if y else 0   a

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nums   str tuple  1 2 3    mul nums   nums replace          print eval mul nums

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Here s some performance measurements from my machine  Relevant in case this is performed for small inputs in a long-running loop   import functools  operator  timeit import numpy as np  def multiply numpy iterable       return np prod np array iterable    def multiply functools iterable       return functools reduce operator mul  iterable   def multiply manual iterable       prod   1     for x in iterable          prod    x      return prod  sizesToTest    5  10  100  1000  10000  100000   for size in sizesToTest      data    1    size      timerNumpy   timeit Timer lambda  multiply numpy data       timerFunctools   timeit Timer lambda  multiply functools data       timerManual   timeit Timer lambda  multiply manual data        repeats   int 5e6   size      resultNumpy   timerNumpy timeit repeats      resultFunctools   timerFunctools timeit repeats      resultManual   timerManual timeit repeats      print f Input size   size  gt 7d  Repeats   repeats  gt 8d     Numpy   resultNumpy  3f   Functools   resultFunctools  3f   Manual   resultManual  3f      Results   Input size        5 Repeats   1000000    Numpy  4 670  Functools  0 586  Manual  0 459 Input size       10 Repeats    500000    Numpy  2 443  Functools  0 401  Manual  0 321 Input size      100 Repeats     50000    Numpy  0 505  Functools  0 220  Manual  0 197 Input size     1000 Repeats      5000    Numpy  0 303  Functools  0 207  Manual  0 185 Input size    10000 Repeats       500    Numpy  0 265  Functools  0 194  Manual  0 187 Input size   100000 Repeats        50    Numpy  0 266  Functools  0 198  Manual  0 185   You can see that Numpy is quite a bit slower on smaller inputs  since it allocates an array before multiplication is performed  Also  watch out for the overflow in Numpy

User · Answer

How about using recursion     def multiply lst       if len lst   gt  1          return multiply lst  -1    lst -1      else          return lst 0

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You can use   import operator import functools functools reduce operator mul   1 2 3 4 5 6   1    See reduce and operator mul documentations for an explanation   You need the import functools line in Python 3

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It is very simple do not import anything  This is my code  This will define a function that multiplies all the items in a list and returns their product   def myfunc lst       multi 1     for product in lst          multi  product     return product

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This is my code   def product list list of numbers       xxx   1     for x in list of numbers          xxx   xxx x     return xxx  print product list  1 2 3 4      result     1 1 2 3 4   24

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Numpy has the prod   function that returns the product of a list  or in this case since it s numpy  it s the product of an array over a given axis   import numpy a    1 2 3 4 5 6  b   numpy prod a       or else you can just import numpy prod     from numpy import prod a    1 2 3 4 5 6  b   prod a

User · Answer

If you want to avoid importing anything and avoid more complex areas of Python  you can use a simple for loop  product   1    Don t use 0 here  otherwise  you ll get zero                 because anything times zero will be zero  list    1  2  3  for x in list      product    x

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The simple way is   import numpy as np np exp np log your array  sum

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I would like this in following way       def product list p             total  1  critical step works for all list           for i in p               total total i   this will ensure that each elements are multiplied by itself           return total    print product list  2 3 4 2    should print 48

User · Answer

the only simple method to understand the logic use for loop     Lap  2 5 7 7 9   x 1  for i in Lap       x i x  print x

User · Answer

Python 3  use functools reduce    gt  gt  gt  from functools import reduce  gt  gt  gt  reduce lambda x  y  x y   1 2 3 4 5 6   720   Python 2  use reduce    gt  gt  gt  reduce lambda x  y  x y   1 2 3 4 5 6   720   For compatible with 2 and 3 use pip install six  then    gt  gt  gt  from six moves import reduce  gt  gt  gt  reduce lambda x  y  x y   1 2 3 4 5 6   720

[python] How can I multiply all items in a list together with Python?

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