循环内部的python调用函数和函数包含if else结构

Question

I have the following python code that call a function that iterate over a dict. the code below not work as expected:

list1=["test1","test2","test3","test4"]
list2=["toto1","test1","test3","toto4"]

def functest(t):
    for l in list2:
        if t == l:
            return cond1
        else:
            return "rien"

for t in list1:
    titi=functest(t)
    print titi

When I print titi var I have toto1 printed 4 times.

If I remove the else inside my function the code seem to work.

How you can explain this behavior ?

Why when I add else with a returned string only the string is printed.

thanks

Answer 1

Because return exits the function and returns your program back to the loop. So when you add the else statement within the loop, the current element of list1 is compared against 'toto1' , enters the else statement, and the function returns "rien" .

def functest(t):
    for l in list2:
        if t == l: 
            return cond1
        else:
            return "rien" # we always end up here on the first iteration, 
                          # when comparing against "toto1"

When you remove the else statement, you loop until you find a match in list2 . However, assuming you still want to return "rien" given that none of the elements in list2 match the element in list1 which is being checked, you should move the return statement out of the loop, so that it is only returned after checking all elements.

def functest(t):
    for l in list2:
        if t == l:
            return "match found"
    return "rien"

Demo

>>> for t in list1:
       titi=functest(t)
       print (titi)

match found
rien
match found
rien

Answer 2

I have tried to modify code in order to implement your logic.

list1=["test1","test2","test3","test4"]
list2=["toto1","test1","test3","toto4"]

def functest(t):
  newReturnList=[]
  for l in list2:
     if t == l:
        newReturnList.append(t+'-found') 
     else:
        newReturnList.append(t+'-NOT found')

return newReturnList


for t in list1:
    titi=functest(t)
   print (titi)