I seem to be missing a crucial piece here.

kratosaurion7

Hi everyone, this is my first post here. I've started python a few days ago and having programmed in VB for a couple years I'm fooled by this new language. There are a couple of concepts that I may be missing. I'm reading "A Byte of Python" which is a very good book, but I don't know why the author did not answer those questions in his book.

1) When I declare a variable in the global field (which I apparently HAVE to give it a value, even if I am only going to decide what value to assign later in the program) and when I modify it from a function it stays the same. Here is an example:
[code]
name = "" #The variable that I want to use later

def getUsrName():

name = raw_input("Please enter your name.
Choice: ") #This is where I assign it a value, but it doesn't modify the global one. Instead working on its own copy.

greetUsr(name) #The workaround I found is to link functions with functions, instead of going through each one in the global field.
[/code]

Also, is it possible to declare a variable but not give it a value ? Because if the user chooses the value of the variable I have to do Value = raw_input("Choose a value") at the declaration time, which is inconvenient.

Any way around those problems?

* I call "Global Field" the place that the code is resting outside every function. I don't know the proper name for this yet

blemidon

You can declare a variable with None value (It's the same as NULL in c), it means 'Nothing':
name = None
for tuples, dirs, arrays you can do this:
t = ()
d = {}
a = []

If you want to change a global var from function, use global:

name = None # it's empty, but declared
def getUsrName():
global name
name = 'someone'

This changes the global name to 'someone'

Hope this helps:
Imre Horvath
Regards: -blemidon-

kratosaurion7

Nice, it worked perfectly ! I wonder why no one bother to explain this stuff in every beginner's book I read >.^ Ah well.

blemidon

Using global vars for getting data from a function is not the preferred way.

You can try:

name = None

def getUsrName():
name = 'someone'
return name

name = getUsrName()

It's nicer.

Regards:
Imre Horvath

blemidon

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acetechcn

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