python变量作用域和列表

python变量作用域和列表

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 = 100def 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)

100100I am in fun99

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)

100I am in fun99100

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 = 1b = 2def 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__': , '__builtins__': , '_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': >, 'exit': , 'quit': , '_': '', '__': '', '___': '', '_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': , '_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 = 100y = 200# 执行x+y# z = x + yz1 = x + yz2 = eval("x+y")print(z1)print(z2)

300300

# exec案例x = 100y = 200# 执行x+y# z = x + yz1 = 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: 300300None

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 = 0def 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) in 10 11 # 调用函数---> 12 fun() in fun() 7 print(x) 8 # 函数自己调用自己----> 9 fun() 10 11 # 调用函数... last 1 frames repeated, from the frame below ... in fun() 7 print(x) 8 # 函数自己调用自己----> 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 Noneprint(fib(3))print(fib(5))print(fib(10))print(fib(-1))print(fib(1))

2555None1

内置数据结构（变量类型）

listsetdicttuple

list（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)

[][100][2, 3, 5, 5, 9, 7, 8][]

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])

2

print(l[0])

3

# 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1print(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 = 100b = 200print(id(a))print(id(b))# a跟c指向同一份数据c = aprint(id(c))a = 101print(a)print(c)print(id(a))print(id(c))

140734817148832140734817152032140734817148832101100140734817148864140734817148832

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

185754007380018575400524881857540052488[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]

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