How to randomly select an item from a list

Question

Assume I have the following list   foo     a    b    c    d    e     What is the simplest way to retrieve an item at random from this list

User · Answer

if you need the index just use   import random foo     a    b    c    d    e   print int random random     len foo   print foo int random random     len foo      random choice does the same

User · Answer

If you want to randomly select more than one item from a list  or select an item from a set  I d recommend using random sample instead   import random group of items    1  2  3  4                  a sequence or set will work here  num to select   2                             set the number to select here  list of random items   random sample group of items  num to select  first random item   list of random items 0  second random item   list of random items 1     If you re only pulling a single item from a list though  choice is less clunky  as using sample would have the syntax random sample some list  1  0  instead of random choice some list    Unfortunately though  choice only works for a single output from sequences  such as lists or tuples    Though random choice tuple some set   may be an option for getting a single item from a set   EDIT  Using Secrets  As many have pointed out  if you require more secure pseudorandom samples  you should use the secrets module   import secrets                                imports secure module  secure random   secrets SystemRandom          creates a secure random object  group of items    1  2  3  4                  a sequence or set will work here  num to select   2                             set the number to select here  list of random items   secure random sample group of items  num to select  first random item   list of random items 0  second random item   list of random items 1    EDIT  Pythonic One-Liner  If you want a more pythonic one-liner for selecting multiple items  you can use unpacking   import random first random item  second random item   random sample group of items  2

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If you want to randomly select more than one item from a list  or select an item from a set  I d recommend using random sample instead   import random group of items    1  2  3  4                  a sequence or set will work here  num to select   2                             set the number to select here  list of random items   random sample group of items  num to select  first random item   list of random items 0  second random item   list of random items 1     If you re only pulling a single item from a list though  choice is less clunky  as using sample would have the syntax random sample some list  1  0  instead of random choice some list    Unfortunately though  choice only works for a single output from sequences  such as lists or tuples    Though random choice tuple some set   may be an option for getting a single item from a set   EDIT  Using Secrets  As many have pointed out  if you require more secure pseudorandom samples  you should use the secrets module   import secrets                                imports secure module  secure random   secrets SystemRandom          creates a secure random object  group of items    1  2  3  4                  a sequence or set will work here  num to select   2                             set the number to select here  list of random items   secure random sample group of items  num to select  first random item   list of random items 0  second random item   list of random items 1    EDIT  Pythonic One-Liner  If you want a more pythonic one-liner for selecting multiple items  you can use unpacking   import random first random item  second random item   random sample group of items  2

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foo     a    b    c    d    e   number of samples   1   In python 2    random items   random sample population foo  k number of samples    In python 3   random items   random choices population foo  k number of samples

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Random item selection   import random  my list    1  2  3  4  5  num selections   2  new list   random sample my list  num selections    To preserve the order of the list  you could do   randIndex   random sample range len my list    n selections  randIndex sort   new list    my list i  for i in randIndex    Duplicate of https   stackoverflow com a 49682832 4383027

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How to randomly select an item from a list  Assume I have the following list  foo     a    b    c    d    e      What is the simplest way to retrieve an item at random from this list   If you want close to truly random  then I suggest secrets choice from the standard library  New in Python 3 6     gt  gt  gt  from secrets import choice           Python 3 only  gt  gt  gt  choice list  abcde     c   The above is equivalent to my former recommendation  using a SystemRandom object from the random module with the choice method - available earlier in Python 2   gt  gt  gt  import random                        Python 2 compatible  gt  gt  gt  sr   random SystemRandom    gt  gt  gt  foo   list  abcde    gt  gt  gt  foo   a    b    c    d    e    And now   gt  gt  gt  sr choice foo   d   gt  gt  gt  sr choice foo   e   gt  gt  gt  sr choice foo   a   gt  gt  gt  sr choice foo   b   gt  gt  gt  sr choice foo   a   gt  gt  gt  sr choice foo   c   gt  gt  gt  sr choice foo   c   If you want a deterministic pseudorandom selection  use the choice function  which is actually a bound method on a Random object    gt  gt  gt  random choice  lt bound method Random choice of  lt random Random object at 0x800c1034 gt  gt   It seems random  but it s actually not  which we can see if we reseed it repeatedly   gt  gt  gt  random seed 42   random choice foo   random choice foo   random choice foo    d    a    b    gt  gt  gt  random seed 42   random choice foo   random choice foo   random choice foo    d    a    b    gt  gt  gt  random seed 42   random choice foo   random choice foo   random choice foo    d    a    b    gt  gt  gt  random seed 42   random choice foo   random choice foo   random choice foo    d    a    b    gt  gt  gt  random seed 42   random choice foo   random choice foo   random choice foo    d    a    b    A comment   This is not about whether random choice is truly random or not  If you fix the seed  you will get the reproducible results -- and that s what seed is designed for  You can pass a seed to SystemRandom  too  sr   random SystemRandom 42   Well  yes you can pass it a  quot seed quot  argument  but you ll see that the SystemRandom object simply ignores it  def seed self   args    kwds        quot Stub method   Not used for a system random number generator  quot      return None

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I propose a script for removing randomly picked up items off a list until it is empty   Maintain a set and remove randomly picked up element  with choice  until list is empty   s set range 1 6   import random  while len s  gt 0    s remove random choice list s      print s    Three runs give three different answers    gt  gt  gt   set  1  3  4  5   set  3  4  5   set  3  4   set  4   set      gt  gt  gt   set  1  2  3  5   set  2  3  5   set  2  3   set  2   set       gt  gt  gt   set  1  2  3  5   set  1  2  3   set  1  2   set  1   set

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This is the code with a variable that defines the random index   import random  foo     a    b    c    d    e   randomindex   random randint 0 len foo -1   print  foo randomindex      print  randomindex    This is the code without the variable   import random  foo     a    b    c    d    e   print  foo random randint 0 len foo -1      And this is the code in the shortest and smartest way to do it   import random  foo     a    b    c    d    e   print random choice foo      python 2 7

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We can also do this using randint   from random import randint l    a   b   c    def get rand element l       if l          return l randint 0 len l -1       else          return None  get rand element l

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The following code demonstrates if you need to produce the same items  You can also specify how many samples you want to extract  The sample method returns a new list containing elements from the population while leaving the original population unchanged  The resulting list is in selection order so that all sub-slices will also be valid random samples    import random as random random seed 0     don t use seed function  if you want different results in each run print random sample foo 3      3 is the number of sample you want to retrieve  Output   d    e    a

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Use random choice    import random  foo     a    b    c    d    e   print random choice foo     For cryptographically secure random choices  e g  for generating a passphrase from a wordlist  use secrets choice    import secrets  foo     battery    correct    horse    staple   print secrets choice foo     secrets is new in Python 3 6  on older versions of Python you can use the random SystemRandom class   import random  secure random   random SystemRandom   print secure random choice foo

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This may already be an answer but you could use random shuffle  Example  import random foo     a    b    c    d    e   random shuffle foo

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You could just   from random import randint  foo     a    b    c    d    e    print foo randint 0 4

User · Answer

How to randomly select an item from a list  Assume I have the following list  foo     a    b    c    d    e      What is the simplest way to retrieve an item at random from this list   If you want close to truly random  then I suggest secrets choice from the standard library  New in Python 3 6     gt  gt  gt  from secrets import choice           Python 3 only  gt  gt  gt  choice list  abcde     c   The above is equivalent to my former recommendation  using a SystemRandom object from the random module with the choice method - available earlier in Python 2   gt  gt  gt  import random                        Python 2 compatible  gt  gt  gt  sr   random SystemRandom    gt  gt  gt  foo   list  abcde    gt  gt  gt  foo   a    b    c    d    e    And now   gt  gt  gt  sr choice foo   d   gt  gt  gt  sr choice foo   e   gt  gt  gt  sr choice foo   a   gt  gt  gt  sr choice foo   b   gt  gt  gt  sr choice foo   a   gt  gt  gt  sr choice foo   c   gt  gt  gt  sr choice foo   c   If you want a deterministic pseudorandom selection  use the choice function  which is actually a bound method on a Random object    gt  gt  gt  random choice  lt bound method Random choice of  lt random Random object at 0x800c1034 gt  gt   It seems random  but it s actually not  which we can see if we reseed it repeatedly   gt  gt  gt  random seed 42   random choice foo   random choice foo   random choice foo    d    a    b    gt  gt  gt  random seed 42   random choice foo   random choice foo   random choice foo    d    a    b    gt  gt  gt  random seed 42   random choice foo   random choice foo   random choice foo    d    a    b    gt  gt  gt  random seed 42   random choice foo   random choice foo   random choice foo    d    a    b    gt  gt  gt  random seed 42   random choice foo   random choice foo   random choice foo    d    a    b    A comment   This is not about whether random choice is truly random or not  If you fix the seed  you will get the reproducible results -- and that s what seed is designed for  You can pass a seed to SystemRandom  too  sr   random SystemRandom 42   Well  yes you can pass it a  quot seed quot  argument  but you ll see that the SystemRandom object simply ignores it  def seed self   args    kwds        quot Stub method   Not used for a system random number generator  quot      return None

User · Answer

Use random choice    import random  foo     a    b    c    d    e   print random choice foo     For cryptographically secure random choices  e g  for generating a passphrase from a wordlist  use secrets choice    import secrets  foo     battery    correct    horse    staple   print secrets choice foo     secrets is new in Python 3 6  on older versions of Python you can use the random SystemRandom class   import random  secure random   random SystemRandom   print secure random choice foo

User · Answer

As of Python 3 6 you can use the secrets module  which is preferable to the random module for cryptography or security uses   To print a random element from a list   import secrets foo     a    b    c    d    e   print secrets choice foo     To print a random index   print secrets randbelow len foo      For details  see PEP 506

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If you also need the index  use random randrange  from random import randrange random index   randrange len foo   print foo random index

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foo     a    b    c    d    e   number of samples   1   In python 2    random items   random sample population foo  k number of samples    In python 3   random items   random choices population foo  k number of samples

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numpy solution  numpy random choice  For this question  it works the same as the accepted answer  import random  random choice     but I added it because the programmer may have imported numpy already  like me   amp  also there are some differences between the two methods that may concern your actual use case   import numpy as np     np random choice foo    randomly selects a single item   For reproducibility  you can do   np random seed 123  np random choice foo    first call will always return  c    For samples of one or more items  returned as an array  pass the size argument   np random choice foo  5             sample with replacement  default  np random choice foo  5  False      sample without replacement

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numpy solution  numpy random choice  For this question  it works the same as the accepted answer  import random  random choice     but I added it because the programmer may have imported numpy already  like me   amp  also there are some differences between the two methods that may concern your actual use case   import numpy as np     np random choice foo    randomly selects a single item   For reproducibility  you can do   np random seed 123  np random choice foo    first call will always return  c    For samples of one or more items  returned as an array  pass the size argument   np random choice foo  5             sample with replacement  default  np random choice foo  5  False      sample without replacement

User · Answer

Use random choice    import random  foo     a    b    c    d    e   print random choice foo     For cryptographically secure random choices  e g  for generating a passphrase from a wordlist  use secrets choice    import secrets  foo     battery    correct    horse    staple   print secrets choice foo     secrets is new in Python 3 6  on older versions of Python you can use the random SystemRandom class   import random  secure random   random SystemRandom   print secure random choice foo

User · Answer

As of Python 3 6 you can use the secrets module  which is preferable to the random module for cryptography or security uses   To print a random element from a list   import secrets foo     a    b    c    d    e   print secrets choice foo     To print a random index   print secrets randbelow len foo      For details  see PEP 506

User · Answer

I propose a script for removing randomly picked up items off a list until it is empty   Maintain a set and remove randomly picked up element  with choice  until list is empty   s set range 1 6   import random  while len s  gt 0    s remove random choice list s      print s    Three runs give three different answers    gt  gt  gt   set  1  3  4  5   set  3  4  5   set  3  4   set  4   set      gt  gt  gt   set  1  2  3  5   set  2  3  5   set  2  3   set  2   set       gt  gt  gt   set  1  2  3  5   set  1  2  3   set  1  2   set  1   set

User · Answer

This may already be an answer but you could use random shuffle  Example  import random foo     a    b    c    d    e   random shuffle foo

User · Answer

The following code demonstrates if you need to produce the same items  You can also specify how many samples you want to extract  The sample method returns a new list containing elements from the population while leaving the original population unchanged  The resulting list is in selection order so that all sub-slices will also be valid random samples    import random as random random seed 0     don t use seed function  if you want different results in each run print random sample foo 3      3 is the number of sample you want to retrieve  Output   d    e    a

User · Answer

You could just   from random import randint  foo     a    b    c    d    e    print foo randint 0 4

User · Answer

This is the code with a variable that defines the random index   import random  foo     a    b    c    d    e   randomindex   random randint 0 len foo -1   print  foo randomindex      print  randomindex    This is the code without the variable   import random  foo     a    b    c    d    e   print  foo random randint 0 len foo -1      And this is the code in the shortest and smartest way to do it   import random  foo     a    b    c    d    e   print random choice foo      python 2 7

User · Answer

We can also do this using randint   from random import randint l    a   b   c    def get rand element l       if l          return l randint 0 len l -1       else          return None  get rand element l

User · Answer

Use random choice    import random  foo     a    b    c    d    e   print random choice foo     For cryptographically secure random choices  e g  for generating a passphrase from a wordlist  use secrets choice    import secrets  foo     battery    correct    horse    staple   print secrets choice foo     secrets is new in Python 3 6  on older versions of Python you can use the random SystemRandom class   import random  secure random   random SystemRandom   print secure random choice foo

User · Answer

If you also need the index  use random randrange  from random import randrange random index   randrange len foo   print foo random index

User · Answer

Random item selection   import random  my list    1  2  3  4  5  num selections   2  new list   random sample my list  num selections    To preserve the order of the list  you could do   randIndex   random sample range len my list    n selections  randIndex sort   new list    my list i  for i in randIndex    Duplicate of https   stackoverflow com a 49682832 4383027

User · Answer

if you need the index just use   import random foo     a    b    c    d    e   print int random random     len foo   print foo int random random     len foo      random choice does the same

[python] How to randomly select an item from a list?

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