On Tuesday 04 December 2012 09:24 AM, Anand Chitipothu wrote:
Python scoping rules when it comes to classes are so confusing.
Can you guess what would be output of the following program?
x = 1
class Foo:
print(x)
Prints the global x
x = x + 1
print(x)
Prints the local x, with the reference to the global x lost in the classes
scope.
print(x, Foo.x)
prints (1, 2) -- ie: the 'global x' and the class local x. So, does the right
thing. What were you expecting ?
Now take the same piece of code and put it in a function.
def f():
x = 1
class Foo:
print(x)
x = x + 1
print(x)
print(x)
print(Foo.x)
f()
Again, global versus local difference for the /class/. Still not sure what you
were expecting,
To add more to your confusion, try this too:
def g():
y = 1
class Foo:
y = 2
def gety(self):
return y
foo = Foo()
print(y, foo.y, foo.gety())
g()
Ok, this is slightly confusing but still consistent. You'd understand the source
of your confusion if you changed the definition for gety() to:
...
...
def gety(self):
return self.y
...
...
Does it make any sense?
Well, it does if you know the rules.
http://effbot.org/pyfaq/what-are-the-rules-for-local-and-global-variables-in-python.htm
Try this:
x = 1
class Foo:
print(x) # this is the global x
x = x + 1 # this is the local x
print(x)
global x # now lets be explicit
print(x, Foo.x)
what happened here ?
cheers,
- steve
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