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變量作用域

變量由作用范圍限制

分類：按照作用域分類

全局(global)：在函數(shù)外部定義
局部(local)：在函數(shù)內(nèi)部定義

變量的作用范圍

全局變量：在整個全局范圍都有效
全局變量在局部可以使用（即函數(shù)內(nèi)部可以訪問函數(shù)外部定義的變量）
局部變量在局部范圍可以使用
局部變量在全局范圍無法使用

LEGB原則

L（Local）局部作用域
E（Enclosing function local）外部嵌套函數(shù)作用域
G（Global module）函數(shù)定義所在模塊作用域
B（Buildin）：python內(nèi)置模塊的作用域

# 認(rèn)為a1是全局的
a1 = 100

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

100
100
I am in fun
99

提升局部變量為全局變量

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)

100
I am in fun
99
100

global，local函數(shù)

可以通過globals和locals顯示出局部變量和全局變量

參考一下案例

# globals 和 locals
# globals 和 locals 叫做內(nèi)建函數(shù)
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': ['', '# 認(rèn)為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)', '# 認(rèn)為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)', '# 認(rèn)為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)', '# 認(rèn)為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)', '# 認(rèn)為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 叫做內(nèi)建函數(shù)\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\\筆記'], 'In': ['', '# 認(rèn)為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)', '# 認(rèn)為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)', '# 認(rèn)為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)', '# 認(rèn)為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)', '# 認(rèn)為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 叫做內(nèi)建函數(shù)\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': '# 認(rèn)為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': '# 認(rèn)為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': '# 認(rèn)為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': '# 認(rèn)為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': '# 認(rèn)為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 叫做內(nèi)建函數(shù)\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()函數(shù)

把一個字符串當(dāng)成一個表達式來執(zhí)行，返回表達式執(zhí)行后的結(jié)果

語法：

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

exec()函數(shù)

跟eval功能類似，但是，不返回結(jié)果

語法：

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

x = 100
y = 200
# 執(zhí)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
# 執(zhí)行x+y
# z = x + y
z1 = x + y
# 1. 注意字符串中引號的寫法
# 2. 比對exec執(zhí)行結(jié)果和代碼執(zhí)行結(jié)果
z2 = exec("print('x+y:',x+y)")

print(z1)
print(z2)

x+y: 300
300
None

遞歸函數(shù)

函數(shù)直接或者間接調(diào)用自身
優(yōu)點：簡潔，理解容易
缺點：對遞歸深度有限制，消耗資源大
python對遞歸深度有限制，超過限制報錯
在寫遞歸程序的時候，一定注意結(jié)束條件

# 遞歸調(diào)用深度限制代碼

x = 0
def fun():
 global x
 x += 1
 print(x)
 # 函數(shù)自己調(diào)用自己
 fun()
 
# 調(diào)用函數(shù)
# fun()

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

RecursionError                            Traceback (most recent call last)

ipython-input-23-bfedb7e396bc> in module>
     10
     11 # 調(diào)用函數(shù)
---> 12 fun()

ipython-input-23-bfedb7e396bc> in fun()
      7     print(x)
      8     # 函數(shù)自己調(diào)用自己
----> 9     fun()
     10
     11 # 調(diào)用函數(shù)

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

ipython-input-23-bfedb7e396bc> in fun()
      7     print(x)
      8     # 函數(shù)自己調(diào)用自己
----> 9     fun()
     10
     11 # 調(diào)用函數(shù)

RecursionError: maximum recursion depth exceeded while calling a Python object

# 斐波那契數(shù)列
# 一列數(shù)字，第一個值是1，第二個也是1，從第三個開始，每一個數(shù)字的值等于前兩個數(shù)字出現(xiàn)的值的和
# 數(shù)學(xué)公式為： 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個數(shù)字的斐波那契數(shù)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

內(nèi)置數(shù)據(jù)結(jié)構(gòu)（變量類型）

list
set
dict
tuple

list（列表）

一組有順序的數(shù)據(jù)的組合

創(chuàng)建列表

空列表

# 1. 創(chuàng)建空列表
l1 = []
# type是內(nèi)置函數(shù)，負(fù)責(zé)打印出變量的類型
print(type(l1))
print(l1)

# 2. 創(chuàng)建帶值的列表
l2 = [100]
print(type(l2))
print(l2)

# 3. 創(chuàng)建列表，帶多個值
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

訪問

使用下標(biāo)操作（索引）
列表的位子是從0開始

分片操作

對列表進行任意一段的截取
l[:]

# 下標(biāo)訪問列表
l = [3,2,5,1,9,8,7]

print(l[1])

2

print(l[0])

3

# 分片操作
# 注意截取的范圍，包含左邊的下標(biāo)值，不包含右邊的下標(biāo)值
print(l[1:4])

# 下標(biāo)值可以為空，如果不寫，左邊下標(biāo)值默認(rèn)為0，右邊下標(biāo)值為最大數(shù)加一，即表示截取到最后一個數(shù)據(jù)
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)
# 分片可以控制增長幅度，默認(rèn)增長幅度為1
print(l[1:6:1])

# 打印從下標(biāo)1開始的數(shù)字，每次隔一個
print(l[1:6:2])

# 下標(biāo)可以超出范圍，超出后不在考慮多余下標(biāo)內(nèi)容
print(l[2:10])

# 下標(biāo)值，增長幅度可以為負(fù)數(shù)
# 為負(fù)數(shù)，表明為從右往左
# 規(guī)定： 數(shù)組最后一個數(shù)字的下標(biāo)是-1

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

# 分片之負(fù)數(shù)下標(biāo)
print(l)

# 下面顯示的是為空，因為默認(rèn)分片總是從左向右截取
print(l[-2:-4])
print(l[-4:-2])

# 如果分片一定左邊值比右邊大，則步長參數(shù)需要使用負(fù)數(shù)
# 此案例為一個list直接正反截取提供了一個思路
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]

分片操作是生成一個新的list

內(nèi)置函數(shù)id，負(fù)責(zé)顯示一個變量或者數(shù)據(jù)的唯一確定編號

# id函數(shù)舉例
a = 100
b = 200
print(id(a))
print(id(b))

# a跟c指向同一份數(shù)據(jù)
c = a
print(id(c))

a = 101
print(a)
print(c)

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

140734817148832
140734817152032
140734817148832
101
100
140734817148864
140734817148832

# 通過id可以直接判斷出分片是重新生成了一份數(shù)據(jù)還是使用同一份數(shù)據(jù)
l = [3,5,6,8,5,43,4,7]
ll = l[:]  # 分片操作
lll = ll
# 如果兩個id值一樣，則表明分片產(chǎn)生的列表是使用的同一地址同一份數(shù)據(jù)
# 否則，則表明分片是重新產(chǎn)生了一份數(shù)據(jù)，即一個新的列表，然后把數(shù)據(jù)拷貝到新列表中
print(id(l))
print(id(ll))
print(id(lll))

# 通過id知道，ll和lll是同一份數(shù)據(jù)，驗證代碼如下
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]

總結(jié)

到此這篇關(guān)于python變量作用域與列表的文章就介紹到這了,更多相關(guān)python變量作用域與列表內(nèi)容請搜索腳本之家以前的文章或繼續(xù)瀏覽下面的相關(guān)文章希望大家以后多多支持腳本之家！

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