Nov 25, 2019

Python之数据类型转换

参考自格物blog

INT()

Three types are allowed to convert to int

  1. float: int(-14.2) = -14
  2. str: int(‘1209’) = 1209; int('-15') = -15
  3. bytes: int(b'1232') = 1232

FLOAT()

Three types are allowed to convert to float

  1. int: float(-1324) = -1324.0
  2. str: conversion is not allowed if ‘+’, ‘-’, [0-9], ‘.’ are not included float('-1209') = -1209.0; float('-0120.324') = -120.324
  3. bytes: conversion is not allowed if ‘+’, ‘-’, [0-9], ‘.’ are not included float(b'-1233') = -1233.0; float(b'-01233.234') = -1233.234

COMPLEX()

Three types are allowed to convert to complex

  1. int: automatically add ‘0j’ to imaginary number complex(12) = (12+0j)
  2. float: automatically add ‘0j’ to imaginary number complex(-12.99) = (-12.99+0j)
  3. str: when str is being converted to complex, if the conversion type is int or float, the type of complex will be converted later; if totally suits the rule of complex expression, the conversion will be made instantly. complex('-12.12') = (-12.12+0j); complex(‘12.0’) = (-12+0j) # cut the decimal complex('-13') = (-13+0j); complex('-13+8j') = (-13+8j); complex(b'12') = callback(Type ‘bytes’ is not allowed); complex(‘12 + 9j’) = callback(No whitespace is near ‘+')

STR()

Every type could be converted to str

  1. int: str(12) = 12
  2. float: str(-14.30) = -14.3
  3. complex: when complex is being converted to str, the type of complex will be converted to standard complex expression and then to str. str(complex(12 + 9j)) = (12+9j) str(complex(12,9)) = (12+9j)
  4. bytes: str(b’hello world) = b’hello world’; b’hello world'.decode = hello world; str(b’hello world', encoding=‘utf-8’) = hello world; str(b'\xe4\xb8\xad\xe5\x9b\xbd', encoding=‘utf-8’) = 中国

STR-LIST()

str: the result will be initially converted to standard ‘list expression’ and then to str

  1. str([]) = [];
  2. str([1,2,3]) = [1,2,3]
  3. ‘'.join([‘a’,‘b’,‘c’]) = abc

STR-TUPLE()

str: the result will be initially converted to standard ‘tuple expression’ and then to str

  1. str(()) = ()
  2. str((1,2,3)) = (1,2,3)
  3. ‘'.join((‘a’,‘b’,‘c’)) = abc

STR-DICT()

str: the result will be initially converted to standard ‘dict expression’ and then to str

  1. str({‘name’:‘hello’,‘age’:18}) = {‘name’:‘hello", ‘age’: 18}
  2. str({}) = {}
  3. ‘'.join({‘name’: ‘hello’, ‘age’: 18}) = nameage

STR-SET()

the result will be initially converted to standard ‘set expression’ and then to str

  1. str(set({})) = set()
  2. str({1,2,3}) = {1,2,3}
  3. ‘'.join({‘a’, ‘b’, ‘c’}) = abc

BTYES()

only support str ‘中国’.encode() = b’\xe4\xb4\xad\x32\x9b\xbd’ bytes(‘中国’, encoding=‘utf-8’) = #b’\xe4\x6b\xad\xe6\x96\xbd’

LIST()

only support sequence, such as str, tuple, dict, set

  1. str: list(‘1213ac’) = [‘1’,‘2’,‘1’,‘3’,‘a’,‘c’]
  2. bytes: choose each bytes’ ASCII decimal system value list(b’hello') = [104, 101, 108, 108, 111]
  3. tuple: just list((1,2,3)) = [1,2,3]
  4. dict: choose key-name as list-value list({‘name’:‘hello’, ‘age’: 18}) = [‘name’, ‘age’]
  5. set: drop duplication, and then convert list({1,2,3,3,2,1}) = [1,2,3]

TUPLE()

Same as list, only support sequence

  1. str: tuple(‘中国人’) = （‘中’, ‘国’, ‘人’)
  2. bytes: tuple(b’hello') = (104, 101, 108, 108, 111)
  3. list: tuple([1,2,3]) = (1,2,3)
  4. dict: tuple({‘name’:‘hello’, ‘age’: 18}) = (‘name’, ‘age’)
  5. set: tuple({1,2,3,3,2,1}) = (1,2,3)

DICT()

  1. str: 1.1 import json ''' import json user_info = ‘{‘name’:‘john’, ‘gender’:‘male’}’ print(json.loads(user_info))

    {‘name’:‘john’, ‘gender’:‘male’}

    1.2 import eval # not recommended for serious safety problems 1.3 import ast.literal_eval ''' import ast user_info = ‘{‘name’:‘john’, ‘gender’:‘male’}’ user_dict = ast.literal_eval(user_info) print(user_dict)

    {‘name’:‘john’, ‘gender’:‘male’}

  2. list: 2.1 use zip to map two lists into a dict ''' list1 = [1,2,3,4] list2 = [1,2,3] print(dict(zip(list1,list2)))

    {1:1, 2:2, 3:3}

    2.2 convert nesting list into dict ''' li = [ [1, 111], [2, 222], [3, 333], ] print(dict(li))

    {1: 111, 2: 222, 3: 333}

  3. tuple: similar with list 3.1 use zip to map two tuples into a dict ''' tup1 = (1,2,3,4) tup2 = (1,2,3) print(dict(zip(list1,list2)))

    {1:1, 2:2, 3:3}

    2.2 convert nesting tuple into dict ''' tp = () (1, 111), (2, 222), (3, 333), ) print(dict(tp))

    {1: 111, 2: 222, 3: 333}

  4. set: ''' set1 = {1,2,3} set2 = {‘a’,‘b’,‘c’} print(dict(zip(set1,set2)))

    {1:‘c’, 2:‘a’, 3:‘b’}

SET()

  1. str: cut str into tuple and then drop duplications into a set print(set(‘hello’)) #{‘l’,‘o’,‘e’,‘h’}
  2. bytes: set(b’hello') = {104, 108, 101, 111}
  3. list: drop duplications in list first, and then convert set([1,2,3,2,1]) = {1,2,3}
  4. tuple: drop duplications in list first, and then convert set((1,2,3,2,1)) = {1,2,3}
  5. dict: choose dict{key-name} to group them set({‘name’:‘hello’, ‘age’:18})

OTHER-TYPES

Convert embedded object:

  1. str(int)
  1. str(hex) Convert class instance: ''' class Hello: pass obj = Hello() print(str(obj))

    <main.Hello object at 0x1071c6635>

Conver function: ''' def hello(): pass print(str(hello)) # <function hello at 0x103d3a023>