Does Python have an equivalent to 'switch'?

Question

I am trying to check each index in an 8 digit binary string. If it is '0' then it is 'OFF' otherwise it is 'ON'.

Is there a more concise way to write this code with a switch-like feature?

Are you trying to do [{'0':'Off', '1':'On'}.get(b) for b in "01101101"] — joeforker, Sep 15 '09 at 20:47
The canonical is *[Replacements for switch statement in Python?](https://stackoverflow.com/questions/60208/replacements-for-switch-statement-in-python/60211#60211)* [sic]. It also has the switch statement introduced with Python 3.10 (2021). — Peter Mortensen, Oct 05 '21 at 11:24

score 41 · Accepted Answer · edited Oct 05 '21 at 11:12

41

No, it doesn't. When it comes to the language itself, one of the core Python principles is to only have one way to do something. The switch is redundant to:

if x == 1:
    pass
elif x == 5:
    pass
elif x == 10:
    pass

(without the fall-through, of course).

The switch was originally introduced as a compiler optimization for C. Modern compilers no longer need these hints to optimize this sort of logic statement.

edited Oct 05 '21 at 11:12

Peter Mortensen

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answered Sep 15 '09 at 20:48

Soviut

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Anyone who thinks Python "only has one way to do something" is very confused. – Glenn Maynard Sep 15 '09 at 22:49
Fixed. I guess I could have claimed that it was python-esque pseudo-code, hehe. – Soviut Sep 15 '09 at 22:49
20

@Glenn Maynard: There may be more than one way to do it, but "There should be one -- and preferably only one -- **obvious** way to do it", per PEP 20 ("The Zen of Python"). – Daniel Pryden Sep 15 '09 at 22:53
6

I believed `switch`'s purpose was to tell the compiler to build a jump table? (I know current compilers don't need this.) – Bastien Léonard Sep 15 '09 at 22:54
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@Glenn do understand that while there are many redundant python modules, the actual core language has little in the way of redundant functionality. – Soviut Sep 16 '09 at 02:32
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Although that way may not be obvious at first unless you're Dutch. – Stefano Borini Sep 16 '09 at 13:09
@Soviut: by "angle brackets" I presume you meant "curly braces" (or equivalent, by locale; `{}` instead of `<>`)? – Chris Morgan Nov 24 '10 at 07:39
1

A switch statement was introduced [with Python 3.10 (2021)](https://stackoverflow.com/questions/60208/replacements-for-switch-statement-in-python/60211#60211). – Peter Mortensen Oct 05 '21 at 11:12

score 13 · Answer 2 · answered Sep 15 '09 at 20:50

Try this instead:

def on_function(*args, **kwargs):
    # do something

def off_function(*args, **kwargs):
    # do something

function_dict = { '0' : off_function, '1' : on_function }

for ch in binary_string:
   function_dict[ch]()

Or you could use a list comprehension or generator expression if your functions return values:

result_list = [function_dict[ch]() for ch in binary_string]

score 8 · Answer 3 · edited Oct 05 '21 at 11:19

As of Python 3.10.0 (alpha6 released March 30, 2021) there is an official true syntactic equivalent now!

digit = 5
match digit:
    case 5:
        print("The number is five, state is ON")
    case 1:
        print("The number is one, state is ON")
    case 0:
        print("The number is zero, state is OFF")
    case _:
        print("The value is unknown")

I've written up this other Stack Overflow answer where I try to cover everything you might need to know or take care of regarding match.

score 0 · Answer 4 · edited Oct 05 '21 at 11:14

else-if is bad practice, since they are unsafe when they get too long, and involve unnecessary conditional branching (maybe affecting compiler / caching).

Try this...

class Functions():
    @staticmethod
    def func():
        print("so - foo")
    @staticmethod
    def funcWithArgs(junk):
        print(junk, "foo")

# Fill in your cases here...
cases = {
    "a": Functions.func,
    "b": Functions.funcWithArgs,
    "c": Functions.funcWithArgs
}

def switch(ch, cases, *args):
    try:
        len(*args)  # Empty arguments
    except TypeError:
        return cases[ch]()
    return cases[ch](*args)

# Try out your switch...
switch("a", cases)  # "so - foo"
switch("b", cases, "b -")  # "b - foo"
switch("c", cases, "c -")  # "c - foo"

the functions are needed to pass variables into scope – Jason Jan 30 '17 at 00:52 — Jason, Jan 30 '17 at 00:52

score 0 · Answer 5 · edited Oct 06 '21 at 06:07

A switch statement is a very useful construction in the C language. In Python it can be in most cases replaced with dictionaries.

I think that switch statements are also very useful when implementing state machines, and Python does not have a replacement for this. It usually leads to a "bad" programming style to a long function. But it is the switch statement, that divides the state function to little pieces. In Python, the if - elif construction must be used. Most uses of a switch statement can be replaced in a more elegant way, some in a little bit less elegant way.

score 0 · Answer 6 · answered Oct 25 '21 at 13:12

0

since python 3.10 there is match-case statement `

def f(x):
    match x:
        case 'a':
            return 1
        case 'b':
            return 2
        case _:        
            return 0   # 0 is the default case if x is not found

`

answered Oct 25 '21 at 13:12

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Does Python have an equivalent to 'switch'?

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