table of Contents
1 return value
def func(arg):
# ....
return 9 # 返回值为9 默认：return None
val = func('adsfadsf')# 1. 让用户输入一段字符串，计算字符串中有多少A字符的个数。有多少个就在文件a.txt中写多少个“李邵奇”。
def get_char_count(data):
sum_counter = 0
for i in data:
if i == 'A':
sum_counter += 1
return sum_counter
def write_file(line):
if len(line) == 0:
return False # 函数执行过程中，一旦遇到return，则停止函数的执行。
with open('a.txt',mode='w',encoding='utf-8') as f:
f.write(line)
return True
content = input('请输入:')
counter = get_char_count(content)
write_data = "李邵奇" * counter
status = write_file(write_data)
if status:
print('写入成功')
else:
print('写入失败')When the function does not return value, default return None.
Execution of internal functions encountered in return is terminated.
def func1():
return "完成" # 函数每次执行到此，就返回；所以下面代码永远不执行。
for i in range(10):
print(i)
func1()
def func2():
for i in range(10):
print(i)
return "完成"
print(666)
func2() # 只打印0return can return any value
Special case: when a plurality of return value returned, the tuple is returned, and the return value is the same as the tuple
def func():
return (1,2,3)
v = func()
print(v)
# 特殊:返回元组
def func():
return 5,8,"alex"
v = func()
print(v)The return action of:. A return value b to terminate execution of the function.
Exercises
# 1. 写函数，计算一个列表中有多少个数字，打印： 列表中有%s个数字。
# 提示：type('x') == int 判断是否是数字。
# 方式一：
def get_list_counter1(data_list):
count = 0
for item in data_list:
if type(item) == int:
count += 1
msg = "列表中有%s个数字" %(count,)
print(msg)
get_list_counter1([1,22,3,'alex',8])
# 方式二：
def get_list_counter2(data_list):
count = 0
for item in data_list:
if type(item) == int:
count += 1
return count
v = get_list_counter1([1,22,3,'alex',8])
msg = "列表中有%s个数字" %(v,)
print(msg)# 2. 写函数，计算一个列表中偶数索引位置的数据构造成另外一个列表，并返回。
# 方式一：
def get_data_list1(arg):
v = arg[::2]
return v
data = get_data_list1([11,22,33,44,55,66])
# 方式二：
def get_data_list2(arg):
v = []
for i in range(0,len(arg)):
if i % 2 == 0:
v.append(arg[i])
return v
data = get_data_list2([11,22,33,44,55,66])# 3. 读取文件，将文件的内容构造成指定格式的数据，并返回。
"""
a.log文件
alex|123|18
eric|uiuf|19
...
目标结构：
a. ["alex|123|18","eric|uiuf|19"] 并返回。
b. [['alex','123','18'],['eric','uiuf','19']]
c. [
{'name':'alex','pwd':'123','age':'18'},
{'name':'eric','pwd':'uiuf','age':'19'},
]
"""
with open('a.log.txt',mode = 'r',encoding = 'utf-8') as f:
data = f.read()
print(data)
def get_file(a):
date1 = []
for i in a.split('\n'):
date1.append(i)
return date1
v1 = get_file(data)
print(v1)
def get_file1(b):
date2 = []
d = []
for i1 in b.split('\n'):
i1 = i1.split('|')
d.append(i1)
date2 += d
return date2
v2 = get_file1(data)
print(v2)
def get_file2(c):
date3 = []
e = {}
for i2 in c.split('\n'):
i2 = i2.split('|')
e['name'] = i2[0]
e['pwd'] = i2[1]
e['age'] = i2[2]
date3.append(e)
return date3
v3 = get_file2(data)
print(v3)- A method of data types in the end there is no return value:
No return value
v = [1,2,3,4] v.append(55) # 无返回值时不用写return了list : append / insert / remove / clear / extend / reverse
dict : update
set : add / discard / update
Just return value
v = 'ddff2dd554cvc' result = '-'.join(v) return result v = {'k1':12,'k2':'ased'} result = v.get('k2') result = v.keys()str : upper / lower / replace / isdecimal / strip / split / startswith / endswith / encode / format / join
list : find / index
dict : keys / values / items / get
set : intersection / union / difference / symmitric_difference
Modify the data return value +
pop
v = [11,22,33,44] result = v.pop(22)Used to remember
Index, has returned slice value
str: split Back to list
strip 返回字符串 replace 返回字符串 join 返回字符串list : append 无
insert 无 remove 无 pop 返回要删除的数据 find 返回索引的位置 index 返回索引的位置dict: keys to get all the key
values 获取所有的值 items 获取所有的键值对 get 索引存在：返回值 ，不存在：返回None
2 Scope
In python file:
py file: global scope
Function: local scope
a = 1 def s1(): x1 = 666 print(x1) print(a) print(b) b = 2 print(a) s1() a = 88888 def s2(): print(a,b) s1() s2()Only data for each scope scopes can call their own, if the scope of the data does not call, you can call the global scope of
Global scope can only be called global
In the global scope of a function you can call (call already exists) with each other, but not directly call scope scope
to sum up:
1. A function is a scope
2. The role of the Look in field data rules: priority to find data in its own scope, he did not go to "parent" -> "parent" -> until the global, the global not on the error. (Scopes nested)
Note: The value of the parent scope in the end is how much?
x = 10 def func(): x = 9 print(x) func()Small exercises
# 示例一 x = 10 def func(): x = 9 print(x) def x1(): x = 999 print(x) func() # 示例二 x = 10 def func(): x = 9 print(x) def x1(): x = 999 print(x) x1() func() # 示例三 x = 10 def func(): x = 9 print(x) def x1(): x = 999 print(x) print(x) x1() func() # 示例四 x = 10 def func(): x = 8 print(x) def x1(): x = 999 print(x) x1() print(x) func() # 示例五 x = 10 def func(): x = 8 print(x) def x1(): print(x) x1() print(x) func() # 示例六 x = 10 def func(): x = 8 print(x) def x1(): print(x) x = 9 x1() x = 10 print(x) func() # 示例七 x = 10 def func(): x = 8 print(x) def x1(): print(x) x1() x = 9 x1() x = 10 print(x) func()3. The role of sub-domain can only be found in the parent's value, the default variable can not be re-parented assignment.
It can not be assigned only to modify the internal variable types
# ##################### name = 'oldboy' def func(): name = 'alex' # 在自己作用域再创建一个这样的值。 print(name) func() print(name) # ##################### name = [1,2,43] def func(): name.append(999) print(name) func() print(name)If you have to add to the global variable global assignment requires (mandatory assignment)
#示例一 name = "老男孩“ def func(): global name name = 'alex' func() print name # 示例二 name = ["老男孩",'alex'] def func(): global name name = '我' func() print(name) # 示例三 name = "老男孩" def func(): name = 'alex' def inner(): global name name = 999 inner() print(name) func() print(name)Variables with nonlocal, first find the parent of the parent of another variable assignment assignment (mandatory assignment)
name = "老男孩" def func(): name = 'alex' def inner(): nonlocal name # 找到上一级的name name = 999 inner() print(name) func() print(name)
Added: All global variables must be uppercase
USER_LIST = [11,22,3]
def func():
name = 'asdf'
USER_LIST.append(12)
USER_LIST.append(name)
func()
print(USER_LIST)3 small high-level function
-
Function name can be used as a variable
def func(): print(123) v1 = func # func代表函数的地址 func() v1（） # v1、func的函数地址相同，执行调用的函数也相同def func(): print(123) func_list = [func, func, func] # func_list[0]() a # func_list[1]() b # func_list[2]() c for item in func_list: # a/b/c的简化形式 v = item() print(v)def func(): print(123) def bar(): print(666) info = {'k1': func, 'k2': bar} info['k1']() # 函数也可以作为字典的值（也可以做为键，但是没有意义） info['k2']()Note: The function is immutable elements of the collection can be done, it can be used as a dictionary key (key but do not make much sense).
集合中可以放多个重复的函数，但只执行一次。（因为集合的特性：不可重复的）Confuse you
def func(): return 123 func_list1 = [func,func,func] func_list2 = [func(),func(),func()] print(func_list1) # 打印的是func的函数地址 print(func_list2) # 打印的是func执行完返回的值 info = { 'k1':func, # 函数的地址 'k2':func(), # 函数执行完返回的值 } print(info)Functions can also be passed as a parameter
def func(arg): print(arg) func(1) func([1,2,3,4]) def show(): return 999 func(show) # 执行函数func，参数为show,show没有+（），表示show没有执行只是代表该函数的地址。def func(arg): v1 = arg() print(v1) def show(): print(666) func(show)def func(arg): v1 = arg() print(v1) def show(): print(666) result = func(show) print(result)Calling multiple functions
def func(): print('花费查询') def bar(): print('语音沟通') def base(): print('xxx') def show(): print('xxx') def test(): print('xxx') info = { 'f1': func, 'f2': bar, 'f3':base, 'f4':show, 'f5':test } choice = input('请选择要选择功能：') function_name = info.get(choice) if function_name: function_name() else: print('输入错误')
Summary: function as a variable: parameter by value / as nested elements to the dictionary, the list
4 senior function
4.1 function can return values do
# 示例一
def func():
print(123)
def bar():
return func
v = bar()
v()
# 示例二
name = 'oldboy'
def func():
print(name)
def bar():
return func
v = bar()
v()
# 示例三
def bar():
def inner():
print(123)
return inner
v = bar()
v()
# 示例四
name = 'oldboy'
def bar():
name = 'alex'
def inner():
print(name)
return inner
v = bar()
v()
# 示例五
name = 'oldboy'
def bar(name):
def inner():
print(name)
return inner
v1 = bar('alex') # { name=alex, inner } # 闭包，为函数创建一块区域（内部变量供自己使用，存储的代码），为他以后执行提供数据。
v2 = bar('eric') # { name=eric, inner }
v1()
v2()
# 示例六
name = 'alex'
def base():
print(name)
def func():
name = 'eric'
base()
func() # {name=eric, }
# 示例七
name = 'alex'
def func():
name = 'eric'
def base():
print(name)
base()
func()
# 示例八
name = 'alex'
def func():
name = 'eric'
def base():
print(name)
return base
base = func()
base()Note: create function by whom and when?
函数是由谁创建的，执行函数就从哪里开始找# 练习题一
info = []
def func():
print(item)
for item in range(10):
info.append(func)
info[0]()
# 练习题二
info = []
def func(i):
def inner():
print(i)
return inner
for item in range(10):
info.append(func(item))
info[0]()
info[1]()
info[4]()4.2 Closures
def func(name):
def inner():
print(name)
return inner
v1 = func('alex')
v1()
v2 = func('eric')
v2()Return value - to analyze memory function execution. (Wherein the closure is a memory)
# 并不是闭包
def func(name)
def inner():
return 123
return inner
# 是闭包需要满足两个条件：1.封装值 2.内层函数需要使用
def func(name)
def inner():
print(name)
return 123
return inner4.3 Higher-order functions
The function passed as a parameter
To function as a return value
Note: The function assignment
Small 4.4 summary
- 1. Analysis of function execution process (function in the end is who created?)
- 2. The closure concept: to create an area for the convenience and function calls for execution to maintain their own data later. (Scenario: decorator / SQLAlchemy source)