Member Avatar for pwnmercury

hello im new with python and i want to you ask a question.
is there any function like switch on C++ ?

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  • Latest Post Latest Post by vegaseat

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A concise, practical summary that extends the earlier replies and adds modern context.

As and suggested, the idiomatic Python alternatives to a C/C++ switch are (a) an if/elif chain for complex conditions and (b) a dispatch table (dictionary) for fixed, discrete cases — ’s point about if/elif is still correct. Since Python 3.10 there is also structural pattern matching (match/case), which provides a readable, switch-like syntax for many use cases. (docs.python.org)

A fast, common dispatch-table pattern (map keys to callables) — useful when actions vary by a discrete input:

def start(): print("start")
def stop():  print("stop")
def status(): print("status")

dispatch = {
    "start": start,
    "stop":  stop,
    "status": status,
}

# call safely with a default
action = dispatch.get(command, lambda: print("unknown command"))
action()

Dictionaries are very fast for key lookup (average O(1)) because CPython uses a resizable hash table; dispatch tables are a widely used, Pythonic approach. (docs.python.org)

For modern Python (3.10+), match/case provides pattern-based branches and can replace long if/elif ladders when matching shapes, literals, or unpacked structures; consult the PEP for semantics and edge cases (bindings, guards, class patterns). Example:

match value:
    case 0:     handle_zero()
    case (x,y): handle_point(x,y)
    case _:     handle_default()

See PEP 634 for the full design rationale. (peps.python.org)

There is no native goto in Python; the language designers recommend structured constructs (loops, functions, returns) and, when needed, exceptions as a controlled way to break out of deeply nested flows. For cross-function or multi-loop escapes, move inner code into a function and return, or raise/handle a custom exception sparingly. (docs.python.org)

Practical note: prefer readable structure (functions + dispatch or match) over trying to emulate low-level jumps.

Recommended Answers

All 18 Replies

Member Avatar for TrustyTony

Standard answer îs that for fixed values use dictionary lookup, otherwise use if...elif...else.. Learn to use 'in' check in condions. If you want we can recode some meaningfull switch using C snippet in Python.

Member Avatar for Beat_Slayer

An if ... elif ... elif ... sequence is a substitute for the switch or case statements found in other languages.

Source

Cheers and Happy coding

Member Avatar for pwnmercury

Thanks to both of you
Just one more question
is there fucntion like goto on C++
I was thinking something with class but i dont know how to call it to code. :D

Member Avatar for TrustyTony

You can use break to get out of loops and continue to continue iteration from next value.

If you want to jump out deeper from loop I recommend to move the inner loops to function and do return from there.

Edited by TrustyTony because: n/a
Member Avatar for pwnmercury

Yea thanks a lot all ! (:

Member Avatar for snippsat

is there fucntion like goto on C++

No,and i hope we never see goto it in python.
http://xkcd.com/292/

Edsger W.Dijkstra wrote this in 1968.

Member Avatar for vegaseat

Switch/case is rather slow in C or C++ and therefore was not implemented in Python. You can however use the much faster dictionary look-up to mimic a switch/case type function ...

# a dictionary switch/case like statement to replace
# multiple if/elif/else statements in Python

def switch_case(case):
    return "You entered " + {
    '1' : "one",
    '2' : "two",
    '3' : "three"
    }.get(case, "an out of range number")

# Python2
#num = raw_input("Input a number between 1 and 3: ")
# Python3
num = input("Input a number between 1 and 3: ")
print( switch_case(num) )

Note: Sorry about the confusing statement above. A C style switch/case statement in Python would have been too slow. To be general, it would have to be usable with all object types and not just be limited to integers and single characters.

Edited by vegaseat because: sorry state
Member Avatar for arkoenig

Switch/case is rather slow in C or C++ and therefore was not implemented in Python.

Switch/case is slow in C or C++? Not in my experience. Do you have evidence to support this claim?

Member Avatar for Beat_Slayer

I think it's easy as making a case and a for loop and testing them.


Cheers and Happy coding

Member Avatar for arkoenig

I think it's easy as making a case and a for loop and testing them.

Assuming you're talking about testing the speed of switch statements: I can test only the compilers I have available, and on those I can see by looking at the machine code that switch statements often generated faster code than could readily be obtained by hand coding.

Moreover, in decades of working with C and C++ compilers, I don't think I've ever encountered one that generates slower code for a switch statement than it does for the corresponding if-else statements.

So when someone makes the blanket claim that switch statements are slow, I think it's up to the person making that claim to prove it.

Member Avatar for vegaseat

Switch/case is slow in C or C++? Not in my experience. Do you have evidence to support this claim?

It is hard to compare a Python dictionary lookup with a C switch/case construct.

You have to think a little out of your box, and put yourself into the shoes of the Python team. Remember that Python is totally object oriented. The C switch/case is very limited in application. I think it's integers and characters only. To be truly useful, the Python switch/case would have to include all types of objects, that's what would have made so slow!

Edited by vegaseat because: types
Member Avatar for arkoenig

It is hard to compare a Python dictionary lookup with a C switch/case construct.
Also switch/case is very limited in application.

Of course.

I was responding to the specific claim that Python does not have switch statements because they're slower in C than if/else statements. I haven't commented on whether I think switch statements might be useful in Python for other reasons.

Member Avatar for vegaseat

Of course.

I was responding to the specific claim that Python does not have switch statements because they're slower in C than if/else statements. I haven't commented on whether I think switch statements might be useful in Python for other reasons.

This is my original statement:

Switch/case is rather slow in C or C++ and therefore was not implemented in Python. You can however use the much faster dictionary look-up to mimic a switch/case type function ...

It does not make any reference to an if/else if construct.

Member Avatar for arkoenig

This is my original statement:
It does not make any reference to an if/else if construct.

There's no other real alternative to switch/case in C or C++.
In particular, on every C or C++ implementation I've seen, the overhead of calling a function is much greater than that of a switch statement, so fetching an element from an array of function pointers is very unlikely to be a more efficient substitute for a switch.

Member Avatar for vegaseat

I think it's easy as making a case and a for loop and testing them.


Cheers and Happy coding

Oh no, the switch/case will be the winner over multiple if/else. However to get the speed, the C switch/case is very limited and the Python team didn't want to limit it to just integers and single characters. You have to remember that C was developed to write operating systems (Unix). Also remember that the Python core is written in C, and those early team members were experts in C and C++.

Come to think of it, C might have borrowed the switch/case concept from Pascal's case statement. Clever anyway!

Edited by vegaseat because: case
Member Avatar for vegaseat

There's no other real alternative to switch/case in C or C++.
In particular, on every C or C++ implementation I've seen, the overhead of calling a function is much greater than that of a switch statement, so fetching an element from an array of function pointers is very unlikely to be a more efficient substitute for a switch.

Python uses the dictionary container internally, and it is highly optimized. Actually the dictionary is the heart of the Python interpreter and avoids fixed memory locations for objects. I am not surprised that the a dictionary look-up won out over any general purpose switch/case construct.

Member Avatar for Beat_Slayer

I never said to compare it with if..elif..else.

Cheers and Happy coding

Member Avatar for vegaseat

I never said to compare it with if..elif..else.

Cheers and Happy coding

I understand, I am just saying that there is no need to compare. In C switch/case is the racecar, if/else is the bicycle.

Enjoy Python!

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