Linked Questions
570 questions linked to/from Short description of the scoping rules
33
votes
7
answers
8k
views
Why can functions in Python print variables in enclosing scope but cannot use them in assignment? [duplicate]
If I run the following code:
x = 1
class Incr:
print(x)
x = x + 1
print(x)
print(x)
It prints:
1
2
1
Okay no problems, that's exactly what I expected. And if I do the following:
x = 1
...
- 13.9k
56
votes
3
answers
8k
views
How references to variables are resolved in Python [duplicate]
This message is a a bit long with many examples, but I hope it
will help me and others to better grasp the full story of variables
and attribute lookup in Python 2.7.
I am using the terms of PEP 227
...
- 987
11
votes
7
answers
5k
views
Can I define a scope anywhere in Python? [duplicate]
Sometimes I find that I have to use functions with long names such as os.path.abspath and os.path.dirname a lot in just a few lines of code. I don't think it's worth littering the global namespace ...
- 60k
15
votes
2
answers
6k
views
Python nonlocal statement in a class definition [duplicate]
I'm trying to perform some analysis of scope in Python 3 source code and I'm stuck with how the nonlocal statement statement works inside a class definition.
As I understand it, the class definition ...
- 6,746
0
votes
2
answers
31k
views
Why "name 'cursor' is not defined" when pyodbc cursor is in main()? [duplicate]
I'm running a Python program, condensed below, from the command line, and it gives me an error (name 'cursor' is not defined) and points to the cursor.fetchmany() row near the bottom. However, the ...
0
votes
1
answer
8k
views
"local variable referenced before assignment" [duplicate]
I come from a land of heavy Java and PHP experience so when it comes to Python much of the rules do not make sense to me.
I have a recursive Fibonacci function below that spits out the error:
...
- 37
5
votes
2
answers
4k
views
Scope of variables declared in main function? [duplicate]
Simple question about variable scope: Why is it that variables declared in the main function are accessible from external functions? I.e. Why does the following print "yes"?
def run():
print ...
- 175
5
votes
3
answers
2k
views
Class vs instance initialization in Python [duplicate]
I am a bit puzzled why when initializing an instance of a class in Python, I cannot use class attributes. Here is the example:
class TestClass:
... shared_list = ['a', 'b', 'c']
... def __init__(self)...
- 506
-1
votes
2
answers
8k
views
NameError: name 'cap' is not defined [duplicate]
I have defined cap in
def fingerCursor(device):
global cap
global cap_height
global cap_width
cap = cv2.VideoCapture(device)
#cap.set(cv2.cap_PROP_FRAME_HEIGHT,720)
#...
-1
votes
3
answers
8k
views
Class NameError: name 'var' is not defined [duplicate]
class Gui():
var = None
def refreshStats(args):
print(str(var))
clas = Gui()
clas.refreshStats()
Trace
File "sample.py", line 5, in refreshStats
print(str(var))
NameError: name '...
5
votes
1
answer
6k
views
How does scope work with try and except blocks in python? [duplicate]
So I am a bit confused about the scoping of variables with try and except blocks. How come my code allows me to use the variables outside of the try block and even the while loop for that matter even ...
- 133
4
votes
2
answers
3k
views
What are the differences (if exist) in variable scope between Python and C++? [duplicate]
I'm a bit confused with the variable scope of Python. Perhaps because of being used to the convention of C++, I always made some mistakes in variable scope of Python. For example:
in C++:
int main(...
- 241
2
votes
1
answer
3k
views
Trying to use variables outside of a for loop gives a SyntaxError: no binding for nonlocal 'max_' found [duplicate]
def min_diff(arry_):
max_ =0
temp_ =0
for i in arry_:
nonlocal max_
nonlocal temp_
if i > max_:
nonlocal max_
nonlocal temp_
temp_ = max_
...
7
votes
1
answer
398
views
Python: Variables are still accessible if defined in try or if? [duplicate]
I'm a Python beginner and I am from C/C++ background. I'm using Python 2.7.
I read this article: A Beginner’s Guide to Python’s Namespaces, Scope Resolution, and the LEGB Rule, and I think I have ...
- 2,586
3
votes
2
answers
854
views
Declare variable as global inside block __name__ == "__main__" [duplicate]
Inside the block
if __name__ == "__main__":
do I need to declare a variable as global in order to set its value?
Or... is this block not a function and hence I don't need to do this?
I ...
- 39.6k