Hi all. I would proposeto you all a switch-case syntax for Python. I already
read PEP 3103 and I'm not completely satisfied by any of the proposed
solutions. This is my proposal:
switch_stmt ::= "switch" identifier "case" expression_list ":" suite
("case" expression_list ":" suite)*
["else" ":" suite]
or, more simply:
switch x case var1:
....
case var2:
...
case var3:
...
else:
...
Expression list should yield an iterable. The case suite will be executed if
the variable of the identifier is a member of the iterable.
For example, in a "switch x" statement, the code "case iterable: " is identical
to "if x in iterable: " (or elif etc). So if you want to perform the same case
block for more than one value, you have only to specify a tuple, a range etc.
I would suggest to add an exception for non-iterable variables, so that you
don't have to write "case var, : " but simply "case var: " and it will be
identical to "if x == var: ". It's a bit tricky but the alternative is ugly.
Fallthrough is disabled by default. The continue keyword cause to skip all the
remaining current case suite. The next case will be checked. You can't use the
continue keyword in the else clause.
Some random remarks:
1. switch is on the same line of the first case. This will avoid any unpythonic
syntaxes like:
switch x
case var1:
...
or
switch x:
case var1:
...
2. Fallthrough is disabled by default because IMHO it's what non-programmers
expect and that's what programmer usually needs more. I don't think a switch
with such a syntax needs a break statement.
3. As an alternative, the continue statement could be written only at the end
of a case suite; it will be less powerful and not consistent with the other
compound statements, but it will improve readability.
4. I decided to not use already existing keyword like "if" or "in", since it
will be misleading and problematic for syntax highlighters.
Tell me what you think about.
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