python 变量作用域和列表

原创

ruochen

修改于 2021-02-22 14:39:39

1.3K0

变量作用域

变量由作用范围限制
分类：按照作用域分类
- 全局(global)：在函数外部定义
- 局部(local)：在函数内部定义
变量的作用范围
- 全局变量：在整个全局范围都有效
- 全局变量在局部可以使用（即函数内部可以访问函数外部定义的变量）
- 局部变量在局部范围可以使用
- 局部变量在全局范围无法使用
LEGB原则
- L（Local）局部作用域
- E（Enclosing function local）外部嵌套函数作用域
- G（Global module）函数定义所在模块作用域
- B（Buildin）：python内置模块的作用域

# 认为a1是全局的
a1 = 100

def fun():
    print(a1)
    print("I am in fun")
    # a2的作用范围是fun
    a2 = 99
    print(a2)
    
print(a1)
fun()
# print(a2)

I am in fun

提升局部变量为全局变量

使用global
案例如下

def fun():
    global b1 
    b1 = 100
    print(b1)
    print("I am in fun")
    b2 = 99
    print(b2)

fun()
print(b1)

I am in fun

global，local函数

可以通过globals和locals显示出局部变量和全局变量
参考一下案例

# globals 和 locals
# globals 和 locals 叫做内建函数
a = 1
b = 2

def fun(c,d):
    e = 111
    print("Locals={0}".format(locals()))
    print("Globals={0}".format(globals()))
          
fun(100, 200)

Locals={'c': 100, 'd': 200, 'e': 111}

/*
* 提示：该行代码过长，系统自动注释不进行高亮。一键复制会移除系统注释 
* Globals={'__name__': '__main__', '__doc__': 'Automatically created module for IPython interactive environment', '__package__': None, '__loader__': None, '__spec__': None, '__builtin__': <module 'builtins' (built-in)>, '__builtins__': <module 'builtins' (built-in)>, '_ih': ['', '# 认为a1是全局的\na1 = 100\n\ndef fun():\n    print(a1)\n    print("I am in fun")\n    a2 = 99\n    print(a2)\n    \nprint(a2)', '# 认为a1是全局的\na1 = 100\n\ndef fun():\n    print(a1)\n    print("I am in fun")\n    a2 = 99\n    print(a2)\n    \nprint(a1)', '# 认为a1是全局的\na1 = 100\n\ndef fun():\n    print(a1)\n    print("I am in fun")\n    a2 = 99\n    print(a2)\n    \nprint(a1)\nfun()\n# print(a2)', '# 认为a1是全局的\na1 = 100\n\ndef fun():\n    print(a1)\n    print("I am in fun")\n    a2 = 99\n    print(a2)\n    \nprint(a1)\nfun()\nprint(a2)', '# 认为a1是全局的\na1 = 100\n\ndef fun():\n    print(a1)\n    print("I am in fun")\n    a2 = 99\n    print(a2)\n    \nprint(a1)\nfun()\n# print(a2)', 'def fun():\n    b1 = 100\n    print(b1)\n    print("I am in fun")\n    b2 = 99\n    print(b2)\n    \nfun()', 'def fun():\n    global b1 = 100\n    print(b1)\n    print("I am in fun")\n    b2 = 99\n    print(b2)\n\nprint(b1)', 'def fun():\n    global b1 \n    b1 = 100\n    print(b1)\n    print("I am in fun")\n    b2 = 99\n    print(b2)\n\nprint(b1)', 'def fun():\n    global b1 \n    b1 = 100\n    print(b1)\n    print("I am in fun")\n    b2 = 99\n    print(b2)\n\nprint(b1)', 'def fun():\n    global b1 \n    b1 = 100\n    print(b1)\n    print("I am in fun")\n    b2 = 99\n    print(b2)\n\nprint(b1)', '# globals 和 locals\na = 1\nb = 2\n\ndef fun(c,d):\n    e = 111\n    print("Locals={0}".format(locals()))\n    print("Globals={0}".format(globals())\n          \nfun(100, 200)', '# globals 和 locals\na = 1\nb = 2\n\ndef fun(c,d):\n    e = 111\n    print("Locals={0}".format(locals()))\n    print("Globals={0}".format(globals()))\n          \nfun(100, 200)', '# globals 和 locals\n# globals 和 locals 叫做内建函数\na = 1\nb = 2\n\ndef fun(c,d):\n    e = 111\n    print("Locals={0}".format(locals()))\n    print("Globals={0}".format(globals()))\n          \nfun(100, 200)'], '_oh': {}, '_dh': ['d:\\Jupyter\\nootbook\\笔记'], 'In': ['', '# 认为a1是全局的\na1 = 100\n\ndef fun():\n    print(a1)\n    print("I am in fun")\n    a2 = 99\n    print(a2)\n    \nprint(a2)', '# 认为a1是全局的\na1 = 100\n\ndef fun():\n    print(a1)\n    print("I am in fun")\n    a2 = 99\n    print(a2)\n    \nprint(a1)', '# 认为a1是全局的\na1 = 100\n\ndef fun():\n    print(a1)\n    print("I am in fun")\n    a2 = 99\n    print(a2)\n    \nprint(a1)\nfun()\n# print(a2)', '# 认为a1是全局的\na1 = 100\n\ndef fun():\n    print(a1)\n    print("I am in fun")\n    a2 = 99\n    print(a2)\n    \nprint(a1)\nfun()\nprint(a2)', '# 认为a1是全局的\na1 = 100\n\ndef fun():\n    print(a1)\n    print("I am in fun")\n    a2 = 99\n    print(a2)\n    \nprint(a1)\nfun()\n# print(a2)', 'def fun():\n    b1 = 100\n    print(b1)\n    print("I am in fun")\n    b2 = 99\n    print(b2)\n    \nfun()', 'def fun():\n    global b1 = 100\n    print(b1)\n    print("I am in fun")\n    b2 = 99\n    print(b2)\n\nprint(b1)', 'def fun():\n    global b1 \n    b1 = 100\n    print(b1)\n    print("I am in fun")\n    b2 = 99\n    print(b2)\n\nprint(b1)', 'def fun():\n    global b1 \n    b1 = 100\n    print(b1)\n    print("I am in fun")\n    b2 = 99\n    print(b2)\n\nprint(b1)', 'def fun():\n    global b1 \n    b1 = 100\n    print(b1)\n    print("I am in fun")\n    b2 = 99\n    print(b2)\n\nprint(b1)', '# globals 和 locals\na = 1\nb = 2\n\ndef fun(c,d):\n    e = 111\n    print("Locals={0}".format(locals()))\n    print("Globals={0}".format(globals())\n          \nfun(100, 200)', '# globals 和 locals\na = 1\nb = 2\n\ndef fun(c,d):\n    e = 111\n    print("Locals={0}".format(locals()))\n    print("Globals={0}".format(globals()))\n          \nfun(100, 200)', '# globals 和 locals\n# globals 和 locals 叫做内建函数\na = 1\nb = 2\n\ndef fun(c,d):\n    e = 111\n    print("Locals={0}".format(locals()))\n    print("Globals={0}".format(globals()))\n          \nfun(100, 200)'], 'Out': {}, 'get_ipython': <bound method InteractiveShell.get_ipython of <ipykernel.zmqshell.ZMQInteractiveShell object at 0x000001B07AF18BA8>>, 'exit': <IPython.core.autocall.ZMQExitAutocall object at 0x000001B07D7398D0>, 'quit': <IPython.core.autocall.ZMQExitAutocall object at 0x000001B07D7398D0>, '_': '', '__': '', '___': '', '_i': '# globals 和 locals\na = 1\nb = 2\n\ndef fun(c,d):\n    e = 111\n    print("Locals={0}".format(locals()))\n    print("Globals={0}".format(globals()))\n          \nfun(100, 200)', '_ii': '# globals 和 locals\na = 1\nb = 2\n\ndef fun(c,d):\n    e = 111\n    print("Locals={0}".format(locals()))\n    print("Globals={0}".format(globals())\n          \nfun(100, 200)', '_iii': 'def fun():\n    global b1 \n    b1 = 100\n    print(b1)\n    print("I am in fun")\n    b2 = 99\n    print(b2)\n\nprint(b1)', '_i1': '# 认为a1是全局的\na1 = 100\n\ndef fun():\n    print(a1)\n    print("I am in fun")\n    a2 = 99\n    print(a2)\n    \nprint(a2)', 'a1': 100, 'fun': <function fun at 0x000001B07D8C41E0>, '_i2': '# 认为a1是全局的\na1 = 100\n\ndef fun():\n    print(a1)\n    print("I am in fun")\n    a2 = 99\n    print(a2)\n    \nprint(a1)', '_i3': '# 认为a1是全局的\na1 = 100\n\ndef fun():\n    print(a1)\n    print("I am in fun")\n    a2 = 99\n    print(a2)\n    \nprint(a1)\nfun()\n# print(a2)', '_i4': '# 认为a1是全局的\na1 = 100\n\ndef fun():\n    print(a1)\n    print("I am in fun")\n    a2 = 99\n    print(a2)\n    \nprint(a1)\nfun()\nprint(a2)', '_i5': '# 认为a1是全局的\na1 = 100\n\ndef fun():\n    print(a1)\n    print("I am in fun")\n    a2 = 99\n    print(a2)\n    \nprint(a1)\nfun()\n# print(a2)', '_i6': 'def fun():\n    b1 = 100\n    print(b1)\n    print("I am in fun")\n    b2 = 99\n    print(b2)\n    \nfun()', '_i7': 'def fun():\n    global b1 = 100\n    print(b1)\n    print("I am in fun")\n    b2 = 99\n    print(b2)\n\nprint(b1)', '_i8': 'def fun():\n    global b1 \n    b1 = 100\n    print(b1)\n    print("I am in fun")\n    b2 = 99\n    print(b2)\n\nprint(b1)', '_i9': 'def fun():\n    global b1 \n    b1 = 100\n    print(b1)\n    print("I am in fun")\n    b2 = 99\n    print(b2)\n\nprint(b1)', '_i10': 'def fun():\n    global b1 \n    b1 = 100\n    print(b1)\n    print("I am in fun")\n    b2 = 99\n    print(b2)\n\nprint(b1)', '_i11': '# globals 和 locals\na = 1\nb = 2\n\ndef fun(c,d):\n    e = 111\n    print("Locals={0}".format(locals()))\n    print("Globals={0}".format(globals())\n          \nfun(100, 200)', '_i12': '# globals 和 locals\na = 1\nb = 2\n\ndef fun(c,d):\n    e = 111\n    print("Locals={0}".format(locals()))\n    print("Globals={0}".format(globals()))\n          \nfun(100, 200)', 'a': 1, 'b': 2, '_i13': '# globals 和 locals\n# globals 和 locals 叫做内建函数\na = 1\nb = 2\n\ndef fun(c,d):\n    e = 111\n    print("Locals={0}".format(locals()))\n    print("Globals={0}".format(globals()))\n          \nfun(100, 200)'}
*/

eval()函数

把一个字符串当成一个表达式来执行，返回表达式执行后的结果
语法：

            eval(string_code, globals=None, locals=None)

exec()函数

跟eval功能类似，但是，不返回结果
语法：

            exec(string_code, globals=None, locals=None)

x = 100
y = 200
# 执行x+y
# z = x + y
z1 = x + y
z2 = eval("x+y")

print(z1)
print(z2)

# exec案例
x = 100
y = 200
# 执行x+y
# z = x + y
z1 = x + y
# 1. 注意字符串中引号的写法
# 2. 比对exec执行结果和代码执行结果
z2 = exec("print('x+y:',x+y)")

print(z1)
print(z2)

x+y: 300

None

递归函数

函数直接或者间接调用自身
优点：简洁，理解容易
缺点：对递归深度有限制，消耗资源大
python对递归深度有限制，超过限制报错
在写递归程序的时候，一定注意结束条件

# 递归调用深度限制代码

x = 0
def fun():
    global x
    x += 1
    print(x)
    # 函数自己调用自己
    fun()
    
# 调用函数
# fun()

---------------------------------------------------------------------------

RecursionError                            Traceback (most recent call last)

<ipython-input-23-bfedb7e396bc> in <module>

     11 # 调用函数

---> 12 fun()

<ipython-input-23-bfedb7e396bc> in fun()

      7     print(x)

      8     # 函数自己调用自己

----> 9     fun()

     11 # 调用函数

... last 1 frames repeated, from the frame below ...

<ipython-input-23-bfedb7e396bc> in fun()

      7     print(x)

      8     # 函数自己调用自己

----> 9     fun()

     11 # 调用函数

RecursionError: maximum recursion depth exceeded while calling a Python object

# 斐波那契数列
# 一列数字，第一个值是1，第二个也是1，从第三个开始，每一个数字的值等于前两个数字出现的值的和
# 数学公式为： f(1) = 1, f(2) = 1, f(n) = f(n - 1) + f(n - 2)
# 例如： 1，1，2，3，5，8，13....

# n表示求第n个数字的斐波那契数列的值
def fib(n):
    if n == 1 or n == 2:
        return 1
    elif n > 0:
        return fib(n-1) + fib(n-2)
    else:
        return None

print(fib(3))
print(fib(5))
print(fib(10))
print(fib(-1))
print(fib(1))

None

内置数据结构（变量类型）

list
set
dict
tuplelist（列表）
一组有顺序的数据的组合
创建列表
- 空列表

# 1. 创建空列表
l1 = []
# type是内置函数，负责打印出变量的类型
print(type(l1))
print(l1)

# 2. 创建带值的列表
l2 = [100]
print(type(l2))
print(l2)

# 3. 创建列表，带多个值
l3 = [2,3,5,5,9,7,8,]
print(type(l3))
print(l3)

# 4. 使用list()
l4 = list()
print(type(l4))
print(l4)

<class 'list'>

[]

<class 'list'>

[100]

<class 'list'>

[2, 3, 5, 5, 9, 7, 8]

<class 'list'>

[]

列表常用操作

访问
- 使用下标操作（索引）
- 列表的位子是从0开始
分片操作
- 对列表进行任意一段的截取
- l:

# 下标访问列表
l = [3,2,5,1,9,8,7]

print(l[1])

print(l[0])

# 分片操作
# 注意截取的范围，包含左边的下标值，不包含右边的下标值
print(l[1:4])

# 下标值可以为空，如果不写，左边下标值默认为0，右边下标值为最大数加一，即表示截取到最后一个数据
print(l[:])
print(l[:4])
print(l[2:])

[2, 5, 1]

[3, 2, 5, 1, 9, 8, 7]

[3, 2, 5, 1]

[5, 1, 9, 8, 7]

print(l)
# 分片可以控制增长幅度，默认增长幅度为1
print(l[1:6:1])

# 打印从下标1开始的数字，每次隔一个
print(l[1:6:2])

# 下标可以超出范围，超出后不在考虑多余下标内容
print(l[2:10])

# 下标值，增长幅度可以为负数
# 为负数，表明为从右往左
# 规定： 数组最后一个数字的下标是-1

[3, 2, 5, 1, 9, 8, 7]

[2, 5, 1, 9, 8]

[2, 1, 8]

[5, 1, 9, 8, 7]

# 分片之负数下标
print(l)

# 下面显示的是为空，因为默认分片总是从左向右截取
print(l[-2:-4])
print(l[-4:-2])

# 如果分片一定左边值比右边大，则步长参数需要使用负数
# 此案例为一个list直接正反截取提供了一个思路
print(l[-2:-4:-1])
print(l[-1:-8:-1])

[3, 2, 5, 1, 9, 8, 7]

[]

[1, 9]

[8, 9]

[7, 8, 9, 1, 5, 2, 3]

分片操作是生成一个新的list

内置函数id，负责显示一个变量或者数据的唯一确定编号

# id函数举例
a = 100
b = 200
print(id(a))
print(id(b))

# a跟c指向同一份数据
c = a
print(id(c))

a = 101
print(a)
print(c)

print(id(a))
print(id(c))

140734817148832

140734817152032

140734817148832

140734817148864

140734817148832

# 通过id可以直接判断出分片是重新生成了一份数据还是使用同一份数据
l = [3,5,6,8,5,43,4,7]
ll = l[:]     # 分片操作
lll = ll
# 如果两个id值一样，则表明分片产生的列表是使用的同一地址同一份数据
# 否则，则表明分片是重新产生了一份数据，即一个新的列表，然后把数据拷贝到新列表中
print(id(l))
print(id(ll))
print(id(lll))

# 通过id知道，ll和lll是同一份数据，验证代码如下
l[1] = 100
print(l)
print(ll)
print(lll)

ll[1] = 100
print(ll)
print(lll)

1857540073800

1857540052488

1857540052488

[3, 100, 6, 8, 5, 43, 4, 7]

[3, 5, 6, 8, 5, 43, 4, 7]

[3, 5, 6, 8, 5, 43, 4, 7]

[3, 100, 6, 8, 5, 43, 4, 7]

[3, 100, 6, 8, 5, 43, 4, 7]

原创声明：本文系作者授权腾讯云开发者社区发表，未经许可，不得转载。

如有侵权，请联系 cloudcommunity@tencent.com 删除。

python

面向对象编程

原创声明：本文系作者授权腾讯云开发者社区发表，未经许可，不得转载。

如有侵权，请联系 cloudcommunity@tencent.com 删除。

python

面向对象编程

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python 变量作用域和列表

python 变量作用域和列表

变量作用域

提升局部变量为全局变量

global，local函数

eval()函数

exec()函数

递归函数

内置数据结构（变量类型）

列表常用操作

分片操作是生成一个新的list

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