How to create random string using user-inputted characters (Python 3)
Question:
My code looks like this:
char = input('Characters: ')
length = int(input('Length: '))
I want to make a length long string which uses randomly selected characters from the char variable. How can I do this?
Answers:
You can simply use choice from random library
import random
char = input('Characters: ')
list_array = [char for char in char]
length = int(input('Length: '))
my_str = ""
for i in range(length):
my_str += random.choice(char)
print(my_str)
You can use random.choice to choose 1 random character for length times.
Here are some potential answers:
With for loops:
import random
chars = input("Characters: ")
length = int(input("Length: "))
result = ''
for _ in range(length):
result += random.choice(chars)
or
with list comps:
import random
chars = input("Characters: ")
length = int(input("Length: "))
result = ''.join([random.choice(chars) for _ in range(length)])
You’ll get the random string in result
Assuming that the same character can appear several times in char but that the probability with which this character can appear in the generated string should be the same as for any other character, I would suggest to convert the inputted character string to a set (for uniqueness), then to a list, and then use the choice function from the random module in a loop for the desired number of times:
from random import choice
char = input('Characters: ')
char_list = list(set(char))
generated_string = ""
length = int(input('Length: '))
for i in range(length):
generated_string += choice(char_list)
print(generated_string)
TL;DR
In one line, without the need for any for loop
import random
mylongstring=''.join(random.choices(char, k=length)) # If non-unique sampling is needed
mylongstring=''.join(random.sample(char, k=length)) # If Unique elements from string are required
Explanation
You can use random.choices with k equal to you string length. It extracts randomly k elements from your generating iterable element (and string is naturally a sequence of characters). Then you can join your new list.
If you use random.sample instead, the sampling is performed uniquely (each character is extracted only once from your char)
The code is here (note that I fixed char and length just for easy testing purposes)
char = 'mystring'
length = 20
import random
mylonglist = random.choices(char, k=length)
mylongstring=''.join(mylonglist)
print(mylongstring)
# result printed: isngmgstssyinismnsrt
# for unique sampling
length=5
mylonglist = random.sample(char, k=length)
mylongstring=''.join(mylonglist)
print(mylongstring)
# printed: irtgs
Here you find the doc for random.choices and for random.sample
Within the module random in numpy, the choice function allows you to manage the cases with and without replacement (in simple words, can the characters in char string be picked more than or only once?):
import numpy as np
my_string = "hello"
print(np.random.choice(list(my_string), 3, replace=False))
OUTPUT
lol
Note that, if replace=True, you can only request for a number of characters not greater than the length of my_string, otherwise a ValueError will be thrown:
ValueError: Cannot take a larger sample than population when 'replace=False'
Without any extra imports and using the fact that set "unorders" the collection.
chars = input('Characters: ')
length = int(input('Length: '))
random_str = ''.join(c for _, c in set(enumerate(chars)))[:length])
Notice: at each execution the random_str will be different and its result cannot be predicted. This could be annoying in a testing phase. Instead, if using for example random.choice you should first fix the "randomness" by setting the random.seed(n) so, the result at each execution will be the same.
My code looks like this:
char = input('Characters: ')
length = int(input('Length: '))
I want to make a length long string which uses randomly selected characters from the char variable. How can I do this?
You can simply use choice from random library
import random
char = input('Characters: ')
list_array = [char for char in char]
length = int(input('Length: '))
my_str = ""
for i in range(length):
my_str += random.choice(char)
print(my_str)
You can use random.choice to choose 1 random character for length times.
Here are some potential answers:
With for loops:
import random
chars = input("Characters: ")
length = int(input("Length: "))
result = ''
for _ in range(length):
result += random.choice(chars)
or
with list comps:
import random
chars = input("Characters: ")
length = int(input("Length: "))
result = ''.join([random.choice(chars) for _ in range(length)])
You’ll get the random string in result
Assuming that the same character can appear several times in char but that the probability with which this character can appear in the generated string should be the same as for any other character, I would suggest to convert the inputted character string to a set (for uniqueness), then to a list, and then use the choice function from the random module in a loop for the desired number of times:
from random import choice
char = input('Characters: ')
char_list = list(set(char))
generated_string = ""
length = int(input('Length: '))
for i in range(length):
generated_string += choice(char_list)
print(generated_string)
TL;DR
In one line, without the need for any for loop
import random
mylongstring=''.join(random.choices(char, k=length)) # If non-unique sampling is needed
mylongstring=''.join(random.sample(char, k=length)) # If Unique elements from string are required
Explanation
You can use random.choices with k equal to you string length. It extracts randomly k elements from your generating iterable element (and string is naturally a sequence of characters). Then you can join your new list.
If you use random.sample instead, the sampling is performed uniquely (each character is extracted only once from your char)
The code is here (note that I fixed char and length just for easy testing purposes)
char = 'mystring'
length = 20
import random
mylonglist = random.choices(char, k=length)
mylongstring=''.join(mylonglist)
print(mylongstring)
# result printed: isngmgstssyinismnsrt
# for unique sampling
length=5
mylonglist = random.sample(char, k=length)
mylongstring=''.join(mylonglist)
print(mylongstring)
# printed: irtgs
Here you find the doc for random.choices and for random.sample
Within the module random in numpy, the choice function allows you to manage the cases with and without replacement (in simple words, can the characters in char string be picked more than or only once?):
import numpy as np
my_string = "hello"
print(np.random.choice(list(my_string), 3, replace=False))
OUTPUT
lol
Note that, if replace=True, you can only request for a number of characters not greater than the length of my_string, otherwise a ValueError will be thrown:
ValueError: Cannot take a larger sample than population when 'replace=False'
Without any extra imports and using the fact that set "unorders" the collection.
chars = input('Characters: ')
length = int(input('Length: '))
random_str = ''.join(c for _, c in set(enumerate(chars)))[:length])
Notice: at each execution the random_str will be different and its result cannot be predicted. This could be annoying in a testing phase. Instead, if using for example random.choice you should first fix the "randomness" by setting the random.seed(n) so, the result at each execution will be the same.