How to switch between multiple variables using an if-else statement in Python

Question

How would I make a switch between multiple variables using a single switch variable?

Update: To clarify the intent is to switch back between these two sets of variables an indefinite amount of times.

When I try this I get the following error.

a1= 'process1'
a2 = 'process2'

b1 = 'action1'
b2 = 'action2'

switch = True # the switch to indicate which set of variables to use
N = 10        # the number of times to switch between the two sets of variables

# alternate between two sets of variables N times
for i in range (N):
    active_process, active_action = a1, b1 if switch else a2, b2

    print("active_process: %s, active_action is: %s" %(active_process, active_action))
    switch = not switch

Traceback:

Traceback (most recent call last):
  File "/home/username/.PyCharm2019.3/config/scratches/scratch_10.py", line 10, in <module>
    active_process, active_action = a1, b1 if switch else a2, b2
ValueError: too many values to unpack (expected 2)

Process finished with exit code 1

You don't need i or switch here: for response, greeting in (a1, b1), (a2, b2):. — chepner
– chepner, Commented Jan 31, 2020 at 22:47
Or perhaps more idiomatic: responses = ['yes', 'no']; greetings = ['hello', 'goodby']; for response, greeting in zip(responses, greetings): — chepner
– chepner, Commented Jan 31, 2020 at 22:48
Thank you for your help. I updated to make more clear the intent of the question. There was a switch between the two sets of variables an indefinite amount of time. — malanb5
– malanb5, Commented Jan 31, 2020 at 23:33
I'd write that as for ap, aa in islice(cycle([(a1,b1), (a2,b2)]), N): (where islice and cycle are imported from itertools). Or if you need/want i, for i, (ap, aa) in zip(range(N), cycle(...)). — chepner
– chepner, Commented Feb 1, 2020 at 1:32
The error comes from precedence issues: (a1, b1) if switch else (a2, b2). — chepner
– chepner, Commented Feb 1, 2020 at 1:33

malanb5 · Accepted Answer · 2020-01-31 23:35:19Z

1

You're making this far too fragile. You have a table of greeting/response values and a Boolean that tell you which to use. Just do this with a direct-access list:

table = [ ("process1", "action1"),
          ("process2" , "action2")
        ]

N = 10
for i in range(10):
    print("%s, the answer is: %s" % table[i %2])

Alternately, use a dict:

table = { True:  ("process1", "action1"),
          False: ("process2" , "action2")
        }
N = 10
for i in range(N):
    print("%s, the answer is: %s" % table[i %2])

edited Jan 31, 2020 at 23:35

malanb5

3343 silver badges15 bronze badges

answered Jan 31, 2020 at 22:45

Prune

78k14 gold badges63 silver badges83 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

malanb5 Over a year ago

The intent was to switch between the two sets of variables an indefinite amount of times. This is easily accomplished if you take the modulo i%2 to reference the index of the table list.

Prune Over a year ago

Yes, it is. I answered the posted question; you updated afterward.

malanb5 Over a year ago

The only change was to update the variables so that they were not quite as misleading as to what the original intent of the question was and to change the number of times to alternate from 2 to 10. Do you mind if I update your answer with the i%2 as the index of table?

malanb5 Over a year ago

Thank you @Prune I don't want to seem that I'm not appreciative of you. You're right a table is more robust!

malanb5 · Accepted Answer · 2020-01-31 23:19:24Z

Using a list to pack and unpack the items gave the desired outcome:

a1= 'process1'
a2 = 'process2'

b1 = 'action1'
b2 = 'action2'

switch = True # the switch to indicate which set of variables to use
N = 10        # the number of times to switch between the two sets of 

# alternate between two sets of variables N times
for i in range (N):
    [active_process, active_action] = [a1, b1] if switch else [a2, b2]

    print("active_process: %s, active_action is: %s" %(active_process, active_action))
    switch = not switch

Output:

active_process: process1, active_action is: action1
active_process: process2, active_action is: action2
active_process: process1, active_action is: action1
active_process: process2, active_action is: action2
active_process: process1, active_action is: action1
active_process: process2, active_action is: action2
active_process: process1, active_action is: action1
active_process: process2, active_action is: action2
active_process: process1, active_action is: action1
active_process: process2, active_action is: action2

Process finished with exit code 0

Collectives™ on Stack Overflow

How to switch between multiple variables using an if-else statement in Python

2 Answers 2

4 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related