Python编程： 局部变量与全局变量

通过关键字global声明为全局变量，可修改全局变量的值

var1 = 1  # 定义全局变量

def  change_val():
    var1 = 5  # 定义局部变量
    print("change_val after val:",var1)

def change_val_by_global():
    global var1  # 声明全局变量
    var1 = 5
    print("change_val_by_global after val:", var1)

print("var1", var1)  # var1 1

change_val()  # change_val after val: 5

print("var1", var1)  # var1 1

change_val_by_global()  # change_val_by_global after val: 5

print("var1", var1)  # var1 5

列表，字典，集合，类都可以在函数中修改

lst = [1, 2, 3]
dct = {"1": "one", "2": "two"}
st = {"1", "2", "3"}

def change():
    lst[0] =5
    dct["2"] = "three"
    st.add("5")

print("lst", lst)
print("dct", dct)
print("st", st)
"""OUT
lst [1, 2, 3]
dct {'1': 'one', '2': 'two'}
st {'1', '2', '3'}
"""
change()

print("lst", lst)
print("dct", dct)
print("st", st)
"""OUT
lst [5, 2, 3]
dct {'1': 'one', '2': 'three'}
st {'1', '2', '5', '3'}
"""