[Tutor] How to make def where arguments are either stated when called or entered via raw_input

[Peter Otten]

David Craig wrote:

> I'm trying to write a function that will either take arguments when the
> function is called, such as myFunc(x,y,z) or if the user does not enter
> any arguments, myFunc() the raw_input function will ask for them. But I
> dont know how to check how many arguments have been entered. My code is
> below. Anyone know how??

You either can use a star argument that causes the function to accept an 
arbitrary number of arguments which are put into a tuple

>>> def f(*args):
...     if not args:
...             x = raw_input("x? ")
...             y = raw_input("y? ")
...             z = raw_input("z? ")
...     else:
...             x, y, z = args
...     print "x=%r, y=%r, z=%r" % (x, y, z)
...
>>> f()
x? alpha
y? beta
z? gamma
x='alpha', y='beta', z='gamma'
>>> f(1, 2, 3)
x=1, y=2, z=3
>>> f(1)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 7, in f
ValueError: need more than 1 value to unpack

or provide default values that cannot occur as normal input:

>>> def f(x=None, y=None, z=None):
...     if x is None: x = raw_input("x? ")
...     if y is None: y = raw_input("y? ")
...     if z is None: z = raw_input("z? ")
...     print "x=%r, y=%r, z=%r" % (x, y, z)
...
>>> f()
x? one
y? two
z? three
x='one', y='two', z='three'
>>> f("ONE", z="THREE")
y? two
x='ONE', y='two', z='THREE'

> def NoiseCorr(file1,file2,500,0.25,0.35):

That's a syntax error. Try to be more careful about the code you are posting 
here.