Python experience: Do not assign values to simple global variables in functions. If you use from a import *

I recently wrote a python program and found a relatively trick place.

------------------------- A. py -------------------------

PWD = None

Def func1 ():
Global PWD
PWD = "pwd"
Print "PWD in func1 is:" + PWD

------------------------- B. py ------------------------

From a import *
Func1 ()
Print "PWD after call func1 () is:" + str (PWD)

The result of executing python B. py is as follows:

PWD in func1 is: pwd
PWD after call func1 () is: None

 

 

At the beginning, I thought that the value assigned to the global variable in the function cannot be passed back, that is

Global PWD only transmits the global variable to the local variable PWD, and then the user is operating on the local variable PWD, but this is not the case

 

The following example shows how to modify the import Statement.

------------------------- B. py ------------------------
Import

A. func1 ()

Print "PWD after call func1 () is:" + str (a. PWD)

 

 

Output

PWD in func1 is: pwd
PWD after call func1 () is: pwd

 

 

Therefore, I guess global can only change the global variables in this module (this py file ).

 

A. py adds a function.

------------------------- A. py ------------------------

PWD = None

Def func1 ():
Global PWD
PWD = "pwd"
Print "PWD in func1 is:" + PWD

Def func2 ():
Global PWD
Print "PWD in func2 is:" + PWD

 

 

------------------------- B. py ------------------------

From a import *

Print dir ()
Func1 ()
Func2 ()

 

 

The output result is

PWD in func1 is: pwd
PWD in func2 is: pwd

 

 

It seems that my conclusion is true:

Global can only change the global variables in this module (this py file ).

 

 

However, if the global variable is of the list or dict type, no problem occurs.

 

 

------------------------- A. py ------------------------

GLIST = ["glist"]

Def func1 ():
Global GLIST
GLIST [0] = "glist changed"

 

------------------------- B. py ------------------------

From a import *

 

Print GLIST [0]

Run python B. py to print

Glist changed

 

 

Conclusion:

It is best not to use "from a import *". Otherwise, you will find that you cannot assign values to simple global variables.