关于python:python-变量作用域和列表

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变量作用域

  • 变量由作用范畴限度

  • 分类：依照作用域分类

    • 全局 (global)：在函数内部定义
    • 部分 (local)：在函数外部定义

  • 变量的作用范畴

    • 全局变量：在整个全局范畴都无效
    • 全局变量在部分能够应用（即函数外部能够拜访函数内部定义的变量）
    • 局部变量在部分范畴能够应用
    • 局部变量在全局范畴无奈应用

  • LEGB 准则

    • L（Local）部分作用域
    • E（Enclosing function local）内部嵌套函数作用域
    • 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 的作用范畴是 fun
    a2 = 99
    print(a2)
    
print(a1)
fun()
# print(a2)
100
100
I am in fun
99

晋升局部变量为全局变量

  • 应用 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)
100
I am in fun
99
100

global，local 函数

  • 能够通过 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}
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后果
  • 语法：

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

exec() 函数

  • 跟 eval 性能相似，然而，不返回后果
  • 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)
300
300



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

print(z1)
print(z2)
x+y: 300
300
None

递归函数

  • 函数间接或者间接调用本身
  • 长处：简洁，了解容易
  • 毛病：对递归深度有限度，耗费资源大
  • python 对递归深度有限度，超过限度报错
  • 在写递归程序的时候，肯定留神完结条件 
# 递归调用深度限度代码

x = 0
def fun():
    global x
    x += 1
    print(x)
    # 函数本人调用本人
    fun()
    
# 调用函数
# fun()
---------------------------------------------------------------------------

RecursionError                            Traceback (most recent call last)

<ipython-input-23-bfedb7e396bc> in <module>
     10 
     11 # 调用函数
---> 12 fun()


<ipython-input-23-bfedb7e396bc> in fun()
      7     print(x)
      8     # 函数本人调用本人
----> 9     fun()
     10 
     11 # 调用函数


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


<ipython-input-23-bfedb7e396bc> in fun()
      7     print(x)
      8     # 函数本人调用本人
----> 9     fun()
     10 
     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呈现的值的和
# 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 示意求第 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))
2
5
55
None
1

内置数据结构（变量类型）

  • list
  • set
  • dict
  • tuple

list（列表）

  • 一组有程序的数据的组合

  • 创立列表

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

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

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

# 4. 应用 list()
l4 = list()
print(type(l4))
print(l4)
<class 'list'>
[]
<class 'list'>
[100]
<class 'list'>
[2, 3, 5, 5, 9, 7, 8]
<class 'list'>
[]

列表罕用操作

  • 拜访

    • 应用下标操作（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[:]
# 下标拜访列表
l = [3,2,5,1,9,8,7]

print(l[1])
2



print(l[0])
3



# 分片操作
# 留神截取的范畴，蕴含右边的下标值，不蕴含左边的下标值
print(l[1:4])

# 下标值能够为空，如果不写，右边下标值默认为 0，左边下标值为最大数加一，即示意截取到最初一个数据
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)
# 分片能够管制增长幅度，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])

# 下标能够超出范围，超出后不在思考多余下标内容
print(l[2:10])

# 下标值，增长幅度能够为正数
# 为正数，表明为从右往左
# 规定：数组最初一个数字的下标是 -1
[3, 2, 5, 1, 9, 8, 7]
[2, 5, 1, 9, 8]
[2, 1, 8]
[5, 1, 9, 8, 7]



# 分片之正数下标
print(l)

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

# 如果分片肯定右边值比左边大，则步长参数须要应用正数
# 此案例为一个 list 间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惟一确定编号 
# 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
101
100
140734817148864
140734817148832



# 通过 id 能够直接判断出分片是从新生成了一份数据还是应用同一份数据
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应用的同一地址同一份数据
# 否则，则表明分片是从新产生了一份数据，即一个新的列表，而后把数据拷贝到新列表中
print(id(l))
print(id(ll))
print(id(lll))

# 通过 id 晓得，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]

正文完
python
发表至： python
2021-02-24
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