Elif-row without else python

问题

Is it possible to write an else at the end of an if-row which only gets executed if none of all the if statements are true? Example:

if foo==5:
    pass
if bar==5:
    pass
if foobar==5:
    pass
else:
    pass

In this example, the else part gets executed if foobar isn't 5, but I want it to be executed if foo, bar and foobar aren't 5. (But, if all statements are true, all of them have to be executed.)

回答1:

I don't think there's any overly elegant way to do this in Python or any other language. You could store the values in a list but that would obfuscate the actual test ifs, e.g.

tests = [bar ==4, foo == 6, foobar == 8]

if tests[0] :
  # do a thing
if tests[1] :
  # Make a happy cheesecake
if tests[2] :
  # Oh, that's sad

if not True in tests :
  # Invade Paris

Or you could set a tracking flag

wereAnyTrue = False

if foo == 4 :
  # Do the washing
  wereAnyTrue = True
if bar == 6 :
  # Buy flowers for girlfriend
  wereAnyTrue = True

# ... etc

if not wereAnyTrue :
  # Eat pizza in underpants

回答2:

How about doing something like this? Making four if statements but the fourth if statement won't be run if one of the other three is run because the other statements change the variable key

key = True

if foo == 5:
    key = False
if bar == 5:
    key = False
if foobar == 5:
    key = False
if key:
    pass # this would then be your else statement

回答3:

Not directly - those three if blocks are separate. You could use nesting, but that would get pretty complex; the neatest way to accomplish this is probably:

if foo == 5:
    ...
if bar == 5:
    ...
if foobar == 5:
    ...
if not any((foo == 5, bar == 5, foobar == 5)):
    ...

回答4:

If all the if statements are for checking for the same value, I would use the following format instead. It would make the code shorter and more readable, IMO

if 5 in (foo, bar, foobar):
    pass
else:
    pass

回答5:

A variation of jonrsharpe's answer would be using chained equality tests. Like so:

if foo != bar != foobar != 5:
    #gets executed if foo, bar and foobar are all not equal to 5

Looks a bit funny, I guess it's up to you to decide which one is more readable. And, obviously, this won't work if one of those variables is supposed to be equal to something different.

Edit: whoops, this won't work. For example 1 != 1 != 3 != 5 returns false, while 1 != 2 != 3 != 5 return true. Sorry

来源：https://stackoverflow.com/questions/24230930/elif-row-without-else-python

标签

python

if-statement