Python之路--Python基础4--内置函数

print(abs(-1))  #绝对值  1

print(all([1, 2, 3, 4, 5]))             #True
print(all([‘‘, 1, 2]))                  #False
#bool为False的情况0、 空、None

print(bin(12345), type(bin(12345)))     #0b11000000111001 <class ‘str‘>

print(chr(97))                          #按照ascll表将数字转换成字符  a
print(ord("a"))                         #按照ascll表将字符转换成数字  97

print(divmod(10, 3))                    #返回（商，余数） (3, 1)

print(id(1))                            #查看内存地址

print(isinstance("123", int))           #False
print(type("123") is str)               #判断数据类型  True


print(len("123"))                       #3
print("123".__len__())                  #计算长度  3

print(pow(2, 3))                        #2的3次方  8
print(pow(2, 3, 3))                     #前两个参数是求次方，后一个参数是取余运算   2

print(type(repr(1234)))                 #将1234转成字符串   <class ‘str‘>
print(type(str(1234)))                  #<class ‘str‘>


l = [1, 2, 3]
for i in reversed(l):                   #倒着打印
    print(i)


print(round(3.5))                       # 四舍五入   4
print(round(3.3))                       # 3


print(l[0:3:2])                         #切片[1, 3]
a = slice(0, 3, 2)
print(l[a])                             #切片[1, 3]


print(sum([1, 2, 3, 4, 5]))             #求和运算 15
print(sum([1, 2, 3, 4, 5]), 100)        #可以设置初始值100， 结果为115
print(sum([], 100))                     #100


print(eval("1+2*3/4"))    #将字符串形式的表达式 解析并执行: 2.5

a = "print(‘hello exec‘)"
exec(a)                   #将字符串形式的代码   解析并执行:hello exec

#compile()#几乎用不到      #把一个代码文件加载进来，按exec和eval的方式解析并执行

def Sayhi():
    name = "YL"
    print(locals())     #打印局部变量  {‘name‘: ‘YL‘}
    print(globals())    #打印全局变量
Sayhi()



#-------------------------------------------------------------------------------------
#map(function, sequence1, sequence2...)
a = map(lambda x: x*x, range(10))
print(a)        #<map object at 0x000001CBF8573A20>
print(list(a))  #[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
#可以处理多个sequence，实现通过function方法对sequence1,sequence1,..进行处理,这就要求function也支持相应数量的参数输入：
a = map(lambda x, y, z: x+y+z, range(10), range(10), range(10))
print(list(a))  #[0, 3, 6, 9, 12, 15, 18, 21, 24, 27]
#------------------------------------------------------------------------------------------


#-------------------------------------------------------------------------------------
#reduce(function, sequence, starting_value)：
#仅能处理一个sequence，starting_value为初始化值，执行顺序为：先将每个sequence内部第一个值和starting_value进行function处理，
#处理的结果再与sequence第二个值进行function处理，直到结束。
#->reduce的function函数必须要输入两个变量才能进行运算
from functools import reduce
print(reduce(lambda x, y: x + y, [2, 3, 4, 5, 6], 1))  #21
#结果为21   执行顺序为---->((((( (1+2) +3)+4)+5)+6))
print(reduce(lambda x, y: x + y, [2, 3, 4, 5, 6]))     #20
#-------------------------------------------------------------------------------------


#------------------------------------------------------------------------------------
# filter(function, sequence)：对sequence中的item依次执行function(item),只能有1个sequence
a = range(10)
b = filter(lambda x: x > 5, a)
print(b)       #<filter object at 0x00000204ADDC0748>
print(list(b)) #[6, 7, 8, 9]

print(list(filter(lambda x: x+5, a)))  #[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
#filter可以看作是过滤函数,貌似并不能修改sequence里面的值

l = [1, 2, 0, 4, 0, 7]
print(list(filter(None, l)))  #当function是None时，返回的是Ture的item：[1, 2, 4, 7]
#-------------------------------------------------------------------------------------


a = list(range(10))
print(a)                #[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
b = list(range(10, 16))
print(b)                #[10, 11, 12, 13, 14, 15]
print(list(zip(a, b)))  #[(0, 10), (1, 11), (2, 12), (3, 13), (4, 14), (5, 15)]



#print
msg = "又回到最初的起点"
f = open("tofile", "w")
print(msg, "记忆中你青涩的脸", sep="|", end="", file=f)  #在文件tofile中写入：又回到最初的起点|记忆中你青涩的脸

import time      #老牛逼了
for i in range(10):
    time.sleep(0.5)
    #print(".")
    print(".", end="", flush=True)

# import sys
# print("---", vars(sys))
# print("...", dir(sys))

# import time
# for n in (100000, 200000, 300000, 400000):
#     data = b‘x‘*n
#     start = time.time()
#     b = data
#     while b:
#         b = b[1:]
#     print(‘bytes‘, n, time.time()-start)
#
# for n in (100000, 200000, 300000, 400000):
#     data = b‘x‘*n
#     start = time.time()
#     b = memoryview(data)
#     while b:
#         b = b[1:]
#     print(‘memoryview‘, n, time.time()-start)