python 学习笔记3

# li = [11,22,33,44]
# def f1(arg):
#     arg.append(55)
#     # li = f1(li)
# f1(li)
# print(li)


# 不太重要
# 是否可以被执行被调用
# def f1():
#     pass
## f1()
# f2 = 123
## f2()
# print(callable(f1))

# print(callable(f2))
# callable()

# ascil码转换列表 相互转换对应关系
# 数字转换成字母
# r = chr(65)
# print(r)
# A

# 字母转换成数字
# n = ord("a")
# print(n)
# 97



#生成字母随机验证码
# import random
# li = []
# for i in range(6):
#     temp = random.randrange(65,91)
#     c = chr(temp)
#     li.append(c)
# result = "".join(li)
# print(result)



# 生成随机数字
# import random
#  1 <= i <5
# i = random.randrange(1,5)
# i = random.randrange(65,91)
# c = chr(i)
# print(c)

# 生成字母
# import random
# li = []
# for i in range(6):
#     temp = random.randrange(65,91)
#     c = chr(temp)
#     li.append(c)
# result = "".join(li)
# print(result)


#生成字母数字，随机生成数字字母
# import random
# li = []
# for i in range(6):
#     if i ==2 or i ==4:
#         num = random.randrange(0,10)
#         li.append(str(num))
#     else:
#         temp = random.randrange(65,91)
#         c = chr(temp)
#         li.append(c)
# result = "".join(li)
# print(result)

#生成字母数字，随机生成数字字母不限制位数
# import random
# li = []
# for i in range(6):
#     r = random.randrange(0,5)
#     if r ==2 or r ==4:
#         num = random.randrange(0,10)
#         li.append(str(num))
#     else:
#         temp = random.randrange(65,91)
#         c = chr(temp)
#         li.append(c)
#
# result = "".join(li)
# print(result)


# compile()编译代码
# python s1.py
# 1、读取文件内容，str到内存
# 2、python内部，把字符串－》编译成 －》特殊代码
# 3、执行代码
# s = "print(123)"
# 编译 single（单行），eval（表达式），exec（python）
# 将字符串编译成python代码
# r = compile(s,"<string>","exec")
# print(r) #<code object <module> at 0x101b1f5d0, file "<string>", line 1>
# exec 执行python代码
# exec(r) # 123
# eval()

# 执行python代码，接收：代码或者字符串
# exec("7+8+9")
# eval 执行表达式，并获取结果
# ret = eval("7+9+8")
# print(ret)


# 执行python代码，继续接收代码或者字符串
# exec("7+9+8")
#执行表达式，并获取结果
# ret = eval("7+9+8")
# print(ret)

# 快速查看，对象提供了哪些功能
# print(dir(dict))
# 查看帮助
# help(list)


# 共：97，每页显示10条，需要多少页
# r = divmod(97,10)
# print(r) 商9 余数7
# r ＝ divmod(100,10)
# print(r[0]) 商
# print(r[1]) 余数


# s = "alex" 对象，"alex" => str

# s = [11,11,11]
# isinstance 用于判断，对象是否是某个类的实例
# r = isinstance(s,list)
# print(r)   返回True



# filter,map

# def f1(args):
#     result = []
#     for item in args:
#         if item > 22:
#             result.append(item)
#     return result
#
# li = [11,22,33,44,55]
# ret = f1(li)
# print(ret) 33,44,55


# filter (函数，可迭代的对象)
# def f2(a):
#     if a > 22:
#         return True
# li = [11,22,33,44,55]
# ret = filter(f2,li)
# print(list(ret))


# filter内部，循环第二个参数
# result = []
# for item in 第二个参数
#     r = 第一个参数(item)
#     if r:
#         result(item)
# return result
# filter , 循环第二个参数，让每个循环元素执行 函数(第一个参数)，如果函数返回值True，表示元素合法

# ret = filter(f2,li)
# print(list(ret))


# 自动return
# f1 = lambda a: a >30
# ret = f1(90)
# print(ret) True

# filter 函数返回True，将元素添加到结果中
#
# li = [11,22,33,44,55]
# result = filter(lambda a:a > 33,li)
# print(list(result))

# li = [11,22,33,44,55]
# def f1(args):
#     result = []
#     for i in args:
#         result.append(100+i)
#
#     return result
# r = f1(li)
# print(list(r))


# map 将函数返回值添加到结果中
# li = [11,22,33,44,55]
# map(函数，可迭代的对象(可以for循环的东西))
# def f2(a):
#     return a + 100
# result = map(f2,li)
# result = map(lambda a: a +200,li)
# print(list(result))
# result = map(lambda a:a + 200,li)
# print(list(result))


# len
# s = "李杰"
# print(len(s))
#
# s = "李杰"
# b =bytes(s,encoding='utf-8')
# print(len(b))

# 2的10次方
# r = pow(2,10)
# print(r)

# 反转
# li = [11,22,1,1]
# li.reverse()
# reversed(li)
# print(li)

# 四舍五入
# r = round(1.8)
# print(r)

# 切片
# s = "sssssssssss"
# print(s[0:2:2])

# 排序
# li = [11,22,3,1,2]
# li.sort()
# print(li)

# zip
# l1 = ["qq",11,22,33]
# l2 = ["aa",11,22,33]
# l3 = ["zz",11,22,33]
# r = zip(l1,l2,l3)
# # print(list(r))
# temp = list(r)[0]
# ret = ' '.join(temp)
# print(ret)