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?
转载于:https://stackoverflow.com/questions/306400/how-to-randomly-select-an-item-from-a-list
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 random.SystemRandom class:
import random
foo = ['battery', 'correct', 'horse', 'staple']
secure_random = random.SystemRandom()
print(secure_random.choice(foo))
If you also need the index, use random.randrange
from random import randrange
random_index = randrange(len(foo))
print(foo[random_index])
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:)
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)>0:
s.remove(random.choice(list(s)))
print(s)
Three runs give three different answers:
>>>
set([1, 3, 4, 5])
set([3, 4, 5])
set([3, 4])
set([4])
set([])
>>>
set([1, 2, 3, 5])
set([2, 3, 5])
set([2, 3])
set([2])
set([])
>>>
set([1, 2, 3, 5])
set([1, 2, 3])
set([1, 2])
set([1])
set([])
import random_necessary
pick = ['Miss','Mrs','MiSs','Miss']
print pick [int(random_necessary.random_necessary() * len(pick))]
I hope that you find this solution helpful.
I did this to get it to work:
import random
pick = ['Random','Random1','Random2','Random3']
print (pick[int(random.random() * len(pick))])
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)
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)
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.
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.
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 using a SystemRandom object from the random module with the choice method:
>>> import random
>>> sr = random.SystemRandom()
>>> foo = list('abcde')
>>> foo
['a', 'b', 'c', 'd', 'e']
And now:
>>> sr.choice(foo)
'd'
>>> sr.choice(foo)
'e'
>>> sr.choice(foo)
'a'
>>> sr.choice(foo)
'b'
>>> sr.choice(foo)
'a'
>>> sr.choice(foo)
'c'
>>> 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):
>>> random.choice
<bound method Random.choice of <random.Random object at 0x800c1034>>
It seems random, but it's actually not, which we can see if we reseed it repeatedly:
>>> random.seed(42); random.choice(foo), random.choice(foo), random.choice(foo)
('d', 'a', 'b')
>>> random.seed(42); random.choice(foo), random.choice(foo), random.choice(foo)
('d', 'a', 'b')
>>> random.seed(42); random.choice(foo), random.choice(foo), random.choice(foo)
('d', 'a', 'b')
>>> random.seed(42); random.choice(foo), random.choice(foo), random.choice(foo)
('d', 'a', 'b')
>>> random.seed(42); random.choice(foo), random.choice(foo), random.choice(foo)
('d', 'a', 'b')
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)
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) & 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
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']
One easy solution if you are looking for something like this:
from random import *
library = ["New York", "Berlin", "Rome"]
for x in range (10):
i = randrange(0,3)
print(library[i])