不能從一個函數內部訪問全局變量在python

Question

下面是我的代碼

global PostgresDatabaseNameSchema 
global RedShiftSchemaName 

PostgresDatabaseNameSchema = None 
RedShiftSchemaName = None 

def check_assign_global_values(): 
    if not PostgresDatabaseNameSchema: 
     PostgresDatabaseNameSchema = "Superman" 
    if not RedShiftSchemaName: 
     RedShiftSchemaName = "Ironman" 

check_assign_global_values() 

但我得到一個錯誤說

Traceback (most recent call last): 
    File "example.py", line 13, in <module> 
    check_assign_global_values() 
    File "example.py", line 8, in check_assign_global_values 
    if not PostgresDatabaseNameSchema: 
UnboundLocalError: local variable 'PostgresDatabaseNameSchema' referenced before assignment 

所以我們不能訪問或設置全局函數內部的變量？

Answer 1

global應該總是在函數內部定義，原因是它告訴函數你想使用全局變量而不是局部變量。你可以這樣做是這樣的：

PostgresDatabaseNameSchema = None 
RedShiftSchemaName = None 

def check_assign_global_values(): 
    global PostgresDatabaseNameSchema, RedShiftSchemaName 
    if not PostgresDatabaseNameSchema: 
     PostgresDatabaseNameSchema = "Superman" 
    if not RedShiftSchemaName: 
     RedShiftSchemaName = "Ironman" 

check_assign_global_values() 

你應該如何使用global一些基本的瞭解。還有很多其他的SO問題可供您搜索。如這個問題Using global variables in a function other than the one that created them。