在Python中实现C类型Switch语句时的困惑

Question

I am trying to implement switch statement in Python by using dictionary ,but i am getting one problem in that.

Below is what i am trying:

print "Enter value of i"
i=eval(raw_input())

j=0
def switch(i):
    print "Hello\n"
    return {True: 'gauw',
            i==1: a(10),
            i==2: a(20),
            }[True]
def a(t):
    global j
    j=t
switch(i)
print j

Output:

Enter value of i

1

20

But i am expecting 10 as output.So,here the main problem is that,it is executing both statement for i==1 & i==2 . Also,I can't use break here.

So how to get desired output?

Answer 1

Y do you complicate yourself? If its just the implementation of switch, use if and elif.

def switch(i):
    if i==1:
        a(10)
    elif i==2: #Even if here wil work, instead of elif
        a(20)
    else:
        return 'gauw'()

Will do the trick

Answer 2

I think your switch should be:

print "Enter value of i"
i=eval(raw_input())

j=0
def switch(i):
    print "Hello\n"
    try:
        return {
                1: a,
                2: b,
                }[i]()
    except:
        // default action here
        return 'gauw'
def a():
    global j
    j=10
def b():
    global j
    j=20
switch(i)
print j

a(10), a(20) are both invoked when the dictionary was built

EDIT Adding a default case since there are people who cares about this.

Answer 3

I'd separate actions from logic, something like this:

action_dict = dict([
    (1, lambda: a(10)),
    (2, lambda: a(20)),
    ])

def switch(value, actions):
    if value in actions:
        return actions[value]()
    return 'gauw'

print "Enter value of i"
i=eval(raw_input())

switch(i, action_dict)