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(gè)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(wèn)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(wú)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(guò)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(gè)字符串當(dāng)成一個(gè)表達(dá)式來(lái)執(zhí)行，返回表達(dá)式執(zhí)行后的結(jié)果
語(yǔ)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(yǔ)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(hào)的寫(xiě)法
# 2. 比對(duì)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(diǎn)：簡(jiǎn)潔，理解容易
- 缺點(diǎn)：對(duì)遞歸深度有限制，消耗資源大
- python對(duì)遞歸深度有限制，超過(guò)限制報(bào)錯(cuò)
- 在寫(xiě)遞歸程序的時(shí)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(gè)值是1，第二個(gè)也是1，從第三個(gè)開(kāi)始，每一個(gè)數(shù)字的值等于前兩個(gè)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(gè)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（列表）
一組有順序的數(shù)據(jù)的組合
創(chuàng)建列表
# 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(gè)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(wèn)
- 使用下標(biāo)操作（索引）
- 列表的位子是從0開(kāi)始
分片操作
- 對(duì)列表進(jìn)行任意一段的截取
- l[:]
# 下標(biāo)訪問(wèn)列表
l = [3,2,5,1,9,8,7]
print(l[1])
2
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(xiě)，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(gè)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(zhǎng)幅度，默認(rèn)增長(zhǎng)幅度為1
print(l[1:6:1])
# 打印從下標(biāo)1開(kāi)始的數(shù)字，每次隔一個(gè)
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(zhǎng)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(gè)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?yàn)槟J(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(zhǎng)參數(shù)需要使用負(fù)數(shù)
# 此案例為一個(gè)list直接正反截取提供了一個(gè)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(gè)新的list
內(nèi)置函數(shù)id，負(fù)責(zé)顯示一個(gè)變量或者數(shù)據(jù)的唯一確定編號(hào)
# 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(guò)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(gè)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(gè)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(guò)id知道，ll和lll是同一份數(shù)據(jù)，驗(yàn)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(qǐng)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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