Python def function: How do you specify the end of the function?
I'm just learning python and confused when a "def" of a function ends?
I see code samples like:
def myfunc(a=4,b=6):
sum = a + b
return sum
myfunc()
I know it doesn't end because of the return (because I've seen if statements... if FOO than return BAR, else return FOOBAR). How does Python know this isn't a recursive function that calls itself? When the function runs does it just keep going through the program until it finds a return? That'd lead to some interesting errors.
Thanks
In Python whitespace is significant. The function ends when the indentation becomes smaller (less).
def f():
pass # first line
pass # second line
pass # <-- less indentation, not part of function f.
Note that one-line functions can be written without indentation, on one line:
def f(): pass
And, then there is the use of semi-colons, but this is not recommended :
def f(): pass; pass
The three forms above show how the end of a function is defined syntactically. As for the semantics, in Python there are three ways to exit a function:
Using the return statement. This works the same as in any other imperative programming language you may know.
Using the yield statement. This means that the function is a generator. Explaining its semantics is beyond the scope of this answer. Have a look at Can somebody explain me the python yield statement?
By simply executing the last statement. If there are no more statements and the last statement is not a return statement, then the function exists as if the last statement were return None . That is to say, without an explicit return statement a function returns None . This function returns None :
def f():
pass
And so does this one:
def f():
42
Python is white-space sensitive in regard to the indentation. Once the indentation level falls back to the level at which the function is defined, the function has ended.
To be precise, a block ends when it encounter a non-empty line indented at most the same level with the start. This non empty line is not part of that block For example, the following print ends two blocks at the same time:
def foo():
if bar:
print "bar"
print "baz" # ends the if and foo at the same time
The indentation level is less-than-or-equal to both the def and the if, hence it ends them both.
Lines with no statement, no matter the indentation, does not matter
def foo():
print "The line below has no indentation"
print "Still part of foo"
But the statement that marks the end of the block must be indented at the same level as any existing indentation. The following, then, is an error:
def foo():
print "Still correct"
print "Error because there is no block at this indentation"
Generally, if you're used to curly braces language, just indent the code like them and you'll be fine.
BTW, the "standard" way of indenting is with spaces only, but of course tab only is possible, but please don't mix them both.
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