What is the difference between "else: return True" and "Return True?"
When I learn Python, I came across some different styles. I'm wondering what the difference is between using "else" as opposed to just putting the code outside of the "if" statement. To further explain my question, here are two blocks of code below.
x = 5
if x == 5:
return True
else:
return False
I understand that this returns False if x! = 5, but how does this code below differ from the code above? Is this the same or is there a slight difference? Is there an advantage to using one over the other?
x = 5
if x == 5:
return True
return False
There is no difference in your code because the part if
ends with a symbol return
if the condition is true and the code will exit anyway. And if the condition is false, the branch else
also ending in will execute return
, so else
not required.
It's a matter of style, but one could argue that the second option is preferable, IMHO easier to read and with less drift to the right - in fact, some languages / compilers will flag it with a warning because it else
would be unnecessary.
The key point here is that when both branches have a conditional end with return
, then else
it is optional. But if it isn't, then you need to use else
, otherwise you end up executing code that was not intended. For example, here you cannot delete else
:
if n > 10:
n = 1
else:
n *= 10
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There is a very slight difference, but this is one you don't really care about. Considering these two features:
def f1():
x = 5
if x == 5:
return True
else:
return False
def f2():
x = 5
if x == 5:
return True
return False
Look at the byte code resulting from each one:
>>> dis.dis(f1)
4 0 LOAD_CONST 1 (5)
2 STORE_FAST 0 (x)
5 4 LOAD_FAST 0 (x)
6 LOAD_CONST 1 (5)
8 COMPARE_OP 2 (==)
10 POP_JUMP_IF_FALSE 16
6 12 LOAD_CONST 2 (True)
14 RETURN_VALUE
8 >> 16 LOAD_CONST 3 (False)
18 RETURN_VALUE
20 LOAD_CONST 0 (None)
22 RETURN_VALUE
>>> dis.dis(f2)
11 0 LOAD_CONST 1 (5)
2 STORE_FAST 0 (x)
12 4 LOAD_FAST 0 (x)
6 LOAD_CONST 1 (5)
8 COMPARE_OP 2 (==)
10 POP_JUMP_IF_FALSE 16
13 12 LOAD_CONST 2 (True)
14 RETURN_VALUE
14 >> 16 LOAD_CONST 3 (False)
18 RETURN_VALUE
For the first function, Python still generates a couple of instructions for the unreachable implied return None
.
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