Is it possible to use functions before declaring their body in python?

Question

Is there any way to make possible to use functions in your file before you actually declare their body?

The following code doesn't seem to work:

abc = myFunction

def myFunction():
    print "123"

Thanks

Answer 1

You can't use the myFunction variable before it's assigned. Your example code is similar to:

def myFunction():
    print abc
    abc = 123

To do what you want, either re-arrange the order:

def myFunction():
    print "123"

abc = myFunction

Or declare abc as just a proxy:

# Style 1
abc = lambda: myFunction()

# Style 2
def abc():
    return myFunction()

def myFunction():
    print "123"

If your function takes parameters, use *args and **kwargs:

# Style 1
abc = lambda *args, **kwargs: myFunction(*args, **kwargs)

# Style 2
def abc(*args, **kwargs):
    return myFunction(*args, **kwargs)

def myFunction(x):
    print x

Answer 2

You can declare functions that use forward declarations, but Python executes the code in your source from top to bottom. So, this would compile and run:

def foo():
    print "in foo"
    bar()

def bar():
    print "in bar"
    foo()

foo()

(except it would cause a stack overflow at runtime, of course). In your example, Python is executing the line

abc = myFunction

before myFunction is defined as anything. You could think of this in terms of typing your source code interactively into the interpreter. When you type in your assignment, you wouldn't have even typed in the definition of myFunction yet, so Python wouldn't be able to refer to it.

Another way to look at this might be the following:

>>> myFunction = "hello"
>>> abc = myFunction
>>> def myFunction():
...     print "there"
... 
>>> abc
'hello'
>>> myFunction
<function myFunction at 0x63270>
>>> myFunction()
there

As you can see, the definition of the myFunction function just changes the binding of the symbol myFunction to a function object.