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python 变量作用域和列表

若尘

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)
100
100
I am in fun
99

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)
100
I am in fun
99
100

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}
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)
300
300


# 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
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>
     10 
     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()
     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 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])
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
101
100
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]


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