In Python, the global keyword is used to use global variables in functions or other local scopes. There are two main reasons for using the global keyword: 1. Modify the value of global variables in a function. 2. Access global variables in functions to avoid UnboundLocalError errors. Example 1: Modify the value of a global variable
python
count = 0
def add():
global count
count += 1
add()
print(count) # 1
If the global keyword is not used here, a local variable count will be created within the function add() and the global variable will not be modified. Example 2: Access global variables
python
count = 0
def print_count():
print(count)
print_count() # 0
But if you try to modify global variables in a function:
python
count = 0
def add_one():
count += 1 # UnboundLocalError
add_one()
At this time, the global keyword must be used:
python
count = 0
def add_one():
global count
count += 1
add_one()
print(count) # 1
To summarize the principles of using global: - If you want to modify global variables inside a function, you need to use a global statement. - If you only access global variables without modifying them, you do not need global. - global only applies to variables, not to other objects such as constants and classes. - Using global will make the code difficult to maintain, so try to avoid using it.