python - How do you create different variable names while in a loop?

Question

This question already has answers here:

How do I create variable variables? (16 answers)

Closed last year.

For example purposes...

for x in range(0,9):
    string'x' = "Hello"

So I end up with string1, string2, string3... all equaling "Hello"

Answer 1

Sure you can; it's called a dictionary:

d = {}
for x in range(1, 10):
    d["string{0}".format(x)] = "Hello"

>>> d["string5"]
'Hello'
>>> d
{'string1': 'Hello',
 'string2': 'Hello',
 'string3': 'Hello',
 'string4': 'Hello',
 'string5': 'Hello',
 'string6': 'Hello',
 'string7': 'Hello',
 'string8': 'Hello',
 'string9': 'Hello'}

I said this somewhat tongue in check, but really the best way to associate one value with another value is a dictionary. That is what it was designed for!

Answer 2

It is really bad idea, but...

for x in range(0, 9):
    globals()['string%s' % x] = 'Hello'

and then for example:

print(string3)

will give you:

Hello

---

However this is bad practice. You should use dictionaries or lists instead, as others propose. Unless, of course, you really wanted to know how to do it, but did not want to use it.

Answer 3

One way you can do this is with exec(). For example:

for k in range(5):
    exec(f'cat_{k} = k*2')

>>> print(cat_0)
0
>>> print(cat_1)
2
>>> print(cat_2)
4
>>> print(cat_3)
6
>>> print(cat_4)
8

Here I am taking advantage of the handy f string formatting in Python 3.6+

Answer 4

It's simply pointless to create variable variable names. Why?

• They are unnecessary: You can store everything in lists, dictionarys and so on
• They are hard to create: You have to use exec or globals()
• You can't use them: How do you write code that uses these variables? You have to use exec/globals() again

Using a list is much easier:

# 8 strings: `Hello String 0, .. ,Hello String 8`
strings = ["Hello String %d" % x for x in range(9)]
for string in strings: # you can loop over them
    print string
print string[6] # or pick any of them

Answer 5

Don't do this use a dictionary

import sys
this = sys.modules[__name__] # this is now your current namespace
for x in range(0,9):
    setattr(this, 'string%s' % x, 'Hello')

print string0
print string1
print string2
print string3
print string4
print string5
print string6
print string7
print string8

don't do this use a dict

globals() has risk as it gives you what the namespace is currently pointing to but this can change and so modifying the return from globals() is not a good idea

Answer 6

for x in range(9):
    exec("string" + str(x) + " = 'hello'")

This should work.

Answer 7

I would use a list:

string = []
for i in range(0, 9):
  string.append("Hello")

This way, you would have 9 "Hello" and you could get them individually like this:

string[x]

Where x would identify which "Hello" you want.

So, print(string[1]) would print Hello.

Answer 8

I think the challenge here is not to call upon global()

I would personally define a list for your (dynamic) variables to be held and then append to it within a for loop. Then use a separate for loop to view each entry or even execute other operations.

Here is an example - I have a number of network switches (say between 2 and 8) at various BRanches. Now I need to ensure I have a way to determining how many switches are available (or alive - ping test) at any given branch and then perform some operations on them.

Here is my code:

import requests
import sys

def switch_name(branchNum):
    # s is an empty list to start with
    s = []
    #this FOR loop is purely for creating and storing the dynamic variable names in s
    for x in range(1,8,+1):
        s.append("BR" + str(branchNum) + "SW0" + str(x))

    #this FOR loop is used to read each of the switch in list s and perform operations on
    for i in s:
        print(i,"\n")
        # other operations can be executed here too for each switch (i) - like SSH in using paramiko and changing switch interface VLAN etc.


def main():  

    # for example's sake - hard coding the site code
    branchNum= "123"
    switch_name(branchNum)


if __name__ == '__main__':
    main()

Output is:

BR123SW01

BR123SW02

BR123SW03

BR123SW04

BR123SW05

BR123SW06

BR123SW07

Answer 9

Using dictionaries should be right way to keep the variables and associated values, and you may use this:

dict_ = {}
for i in range(9):
     dict_['string%s' % i]  = 'Hello'

But if you want to add the variables to the local variables you can use:

for i in range(9):
     exec('string%s = Hello' % i)

And for example if you want to assign values 0 to 8 to them, you may use:

for i in range(9):
     exec('string%s = %s' % (i,i))

Answer 10

Dictionary can contain values and values can be added by using update() method. You want your system to create variables, so you should know where to keep.

variables = {}
break_condition= True # Dont forget to add break condition to while loop if you dont want your system to go crazy.
name = “variable”
i = 0 
name = name + str(i) #this will be your variable name.
while True:
    value = 10 #value to assign
    variables.update(
                  {name:value})
    if break_condition == True:
        break