Built-in functions
Built-in functions (be sure to remember and proficient)
print () screen output
int():pass
str():pass
bool():pass
set(): pass
list () will be converted into a list iterable
tuple () will be converted into a iterable tuple
dict () to create a dictionary corresponding way.
# 创建字典的几种方式 #直接创建 dic = {1: 2} #字典推导式 print({i: 1 for i in range(3)}) dict() #dict创建 dic = dict(one=1, two=2, three=3) print(dic) #fromekeys 方法创建 fromkeys()abs () returns the absolute value of
sum () sums
print(sum([1,2,3])) #4
print(sum((1,2,3),100)) # 104 从100开始算总和- min () for the minimum
通过设置key去使用min
# 返回值是什么就按照什么比较最小的。
例1:
找年龄最小的元组:l1 = [('alex', 73, 170), ('太白', 18, 185), ('武大', 35, 159),]
print(min(l1,key=lambda x:x[1])) #('太白', 18, 185)
#key = 函数名,#min 会自动的将可迭代对象的每一个元素作为实参传给x，
# 将遍历的那个元素即是 ('太白', 18) 返回max () selecting the maximum value
the reversed () for an iterative inversion object, returns an iterator
bytes () the string into bytes Type
bin: to convert decimal to binary and back.
oct: converted to decimal octal string and returns.
hex: decimal converted to a hexadecimal string and returns.
print(bin(10),type(bin(10))) # 0b1010 <class 'str'>
print(oct(10),type(oct(10))) # 0o12 <class 'str'>
print(hex(10),type(hex(10))) # 0xa <class 'str'>zip () method of the slide fastener
lst1 = [1,2,3]
lst2 = ['a','b','c','d']
lst3 = (11,12,13,14,15)
for i in zip(lst1,lst2,lst3):
print(i)
(1, 'a', 11)
(2, 'b', 12)
(3, 'c', 13)sorted sort function
lst=[9,8,6,48,23,615,]
new_lst=sorted(lst) #返回的新列表是经过排序的
print(new_lst) #[6, 8, 9, 23, 48, 615] #原列表不会改变
lst3 = sorted(lst,reverse=True)
print(lst3) #倒叙 与匿名函数配合使用
lst = [{'id':1,'name':'alex','age':18},
{'id':2,'name':'wusir','age':17},
{'id':3,'name':'taibai','age':16},]
print(sorted(lst,key=lambda x:x['age']))
#[{'id': 3, 'name': 'taibai', 'age': 16}, {'id': 2, 'name': 'wusir', 'age': 17}, {'id': 1, 'name': 'alex', 'age': 18}]filtering filtering filter returns a generator
生成器表达式的筛选模式
lst = [{'id':1,'name':'alex','age':18},
{'id':1,'name':'wusir','age':17},
{'id':1,'name':'taibai','age':40},]
print(list(filter(lambda x:x['age']<20,lst)))
#[{'id': 1, 'name': 'alex', 'age': 18}, {'id': 1, 'name': 'wusir', 'age': 17}]
function: 用来筛选的函数,在filter中会自动的把iterable中的元素传递给function,然后根据function返回的True或者False来判断是否保留此项数据map returns an iterator that generates equivalent expressions: cyclic pattern
lst = [1,2,3,4,5]
#生成器表达式的筛选模式
print(list(map(lambda s:s*s,lst))) #[1, 4, 9, 16, 25]reduce
from functools import reduce
'''
第一次：x,y 1,2 求和 3 记录到内存
第二次：x,y 3,3 求和 6 记录到内存
第三次：x,y 6，4 .........
'''
# print(reduce(lambda x,y: x+y,[1,2,3,4,5]))
# print(reduce(lambda x,y: 2*x+y, [1,2,3]))
# print(reduce(lambda x,y: x+y, ['alex','s','b'])) # 可以用字符串拼接Built-in functions (understanding, try to remember)
- eval: type of code execution string, and returns the final result.
eval('2 + 2') # 4
n=81
eval("n + 4") # 85
eval('print(666)') # 666- exec: execution string types.
s = '''
for i in [1,2,3]:
print(i)
'''
exec(s)- help: function module or function for viewing purposes described in detail.
print(help(list))
print(help(str.split))- int: function is used to convert a string or an integer number.
print(int()) # 0
print(int('12')) # 12
print(int(3.6)) # 3
print(int('0100',base=2)) # 将2进制的 0100 转化成十进制。结果为 4- callable: function is used to check whether an object is callable. If it returns True, object may still call fails; but if it returns False, the calling object ojbect will never succeed.
name = 'alex'
def func():
pass
print(callable(name)) # False
print(callable(func)) # True- int: function is used to convert a string or an integer number.
- float: function is used to convert the integer to floating point and string.
- complex: a function to create the complex value real + imag * j or transformed string or a plural number. If the first parameter is a string, there is no need to specify the second parameter. .
- divmod: the divisor and the dividend calculation result, returns a tuple of the quotient and remainder of (a // b, a% b).
- round: retention of floating-point decimal places, default retention integer.
- pow: find the X- the y-th power. (Three parameters of x results of z I y taken)
- bytes: for conversion between different coding.
- ord: Enter the characters to find the position of the character encoding
- chr: Enter the numbers to find out the location of the corresponding character
- repr: Returns a string form of the object (true colors).
# %r 原封不动的写出来
# name = 'taibai'
# print('我叫%r'%name)
# repr 原形毕露
print(repr('{"name":"alex"}'))
print('{"name":"alex"}')- all: iterables in all True is True
- any: iterables, there is a True True