Infinite for loop in Python

Question

I'm new to Python. Actually I implemented something using Java as shown below.

 for(;;){
 switch(expression){
     case c1: statements

     case c2: statements


     default: statement
 }
}

How do I implement this in Python?

score 12 · Accepted Answer · answered Jan 03 '12 at 14:49

12

Use while loop:

 while True:

      if condition1:
            statements
      elif condition2:
            statements
      ...
      else:
            statements

answered Jan 03 '12 at 14:49

soulcheck

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Rob Wouters · Answer 2 · 2012-01-03T14:55:41.973

6

while True:
    # do stuff forever

edited Jan 03 '12 at 14:55

answered Jan 03 '12 at 14:48

Rob Wouters

15,797
3
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score 1 · Answer 3 · answered Jan 03 '12 at 14:55

1

Formally, there's no switch statement in Python; it's a series of nested if-elif-else statements.

Infinite loops are accomplished by the while True statement.

All together:

while True:
    if condition_1:
        condition_1_function
    elif condition_2:
        condition_2_function
    elif condition_3:
        condition_3_function
    else:  # Always executes like "default"
        condition_default_function

answered Jan 03 '12 at 14:55

Makoto

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Beware that there is no fall-through in `if/elif/else` like there would be in `switch` – dcrosta Jan 03 '12 at 15:06

score 1 · Answer 4 · answered Jan 16 '12 at 17:54

1

If you are looking for a way to iterate infinitely in python you can use the itertools.count() function like a for loop. http://docs.python.org/py3k/library/itertools.html#itertools.count

answered Jan 16 '12 at 17:54

tweirick

171
5

This looks useful for infinite generator expressions like `('CONSTANT' for i in itertools.count(0, 0))` as an argument to functions expecting a generator. You don't have to define a separate function that has the while True loop. – hobs Jul 12 '13 at 18:13
@hobs To achieve that, you would use `itertools.repeat('CONSTANT')`. – flornquake Aug 14 '13 at 17:29

score 0 · Answer 5 · answered Jan 03 '12 at 14:52

0

You can use

while True:
    if c1:
        statements
    elif c2:
        statements
    else:
        statements

or

var = 1
while var == 1:
    # do stuff

answered Jan 03 '12 at 14:52

Milo Casagrande

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1

Normally it's more implicit to use the boolean `True` instead of an integer if we're talking infinite loops. This way, the intent is clearer and easier to debug (who's to say that the value of `var` may not change over time?). – Makoto Jan 03 '12 at 14:55
It is true, and using the boolean is (probably) the blessed way. That is just another example of achieving the same thing. `var` can change, but that is also up to the developer to not change it if she chooses to go that way. ;-) – Milo Casagrande Jan 03 '12 at 15:24
1

But why have `var` at all? If the point is to have a value that is always equal to 1 to create an infinite loop, why not just say `while 1 == 1`? And having done that, it's absurd not to just write `while True`. – Ben Jan 03 '12 at 16:16
@Ben: We could go even *further*, and say `while 1`, which is tantamount to `while True`. But that's quite besides the point! :) – Makoto Jan 03 '12 at 17:59

Infinite for loop in Python

5 Answers5