Python数据类型的转换
- 什么是类型转换，为何做类型转换
- 将自身数据类型变成新的数据类型，并拥有新的数据类型的所有功能的过程即为类型转换
- 为方便更好的帮助处理业务，将类型变更为更适合业务场景的类型
1、字符串与数字间的转换
字符串与数字之间转换的要求
str –> number：数字组成的字符串
int_str = '123456' float_str = '3.14'number –> str：无要求
字符串与数字之间转换的函数
原始类型 目标类型 函数 距离 整型 字符串 str new_str = str(123456) 浮点型 字符串 str new_str = str(3.14) 字符串 整型 int new_int = int(‘12’) 字符串 浮点型 float new_float = float(‘1.2’) 
2、字符串与列表间的转换
字符串转列表的函数–split
功能：将字符串以一定规则切割转成列表
用法：string.split(sep=None, maxsplit=-1)
参数：sep: 切割的规则符号，不填写，默认空格， 如字符串无空格则不分割生成列表
maxsplit： 根据切割符号切割的次数， 默认-1无限制
返回值：返回一个列表
In [1]: info = 'my name is david' In [2]: info_list = info.split() In [3]: print(info_list) Out [1]: ['my', 'name', 'is', 'david']列表转字符串的函数–join
功能：将列表以一定规则转成字符串
用法：’sep’.join(iterable)
参数：sep: 生成字符串用来分割列表每个元素的符号
iterable： 非数字类型的列表或元组或集合
In [1]: test = ['a', 'b', 'c'] In [2]: new_str = '.'.join(test) In [3]: print(new_str) Out [1]: 'a.b.c'
3、字符串与bytes的转换
什么是比特类型
二进制的数据流—byte
一种特殊的字符串
字符串前 + b 标记
字符串转bytes的函数—encode
功能：u将字符串转成比特（bytes）类型
用法：string. encode(encoding=’utf-8’, errors=’strict’)
参数：encoding: 转换成的编码格式，如ascii，gbk，默认 utf-8
errors: 出错时的处理方法，默认strict，直接抛错误，也可以选择ignore忽略错误
返回值：返回一个比特（bytes）类型
In [1]: str_data = 'my name is david' In [2]: byte_data = str_data.encode('utf-8') In [3]: print(byte_data) Out [1]: b'my name is david'bytes转字符串的函数–decode
功能：将比特（bytes）类型转成字符串
用法：bytes. decode(encoding=’utf-8’, errors=’strict’)
参数：encoding: 转换成的编码格式，如ascii，gbk，默认 utf-8
errors: 出错时的处理方法，默认strict，直接抛错误，也可以选择ignore忽略错误
返回值：返回一个字符串类型
In [1]: byte_data = b'my name is david' In [2]: str_data = byte_data.decode('utf-8') In [3]: print(str_data) Out [1]: 'my name is david'
4、元组，列表，集合间的转换
列表元组集合之间的转换函数
原始类型 目标类型 函数 举例 列表 集合 set new_set = set([1, 2, 3, 4, 5]) 列表 元组 tuple new_tuple = tuple([1, 2, 3, 4, 5]) 元组 集合 set new_set = set((1, 2, 3, 4, 5)) 元组 列表 list new_list = list((1, 2, 3, 4, 5)) 集合 列表 list new_list = list({1, 2, 3, 4, 5}) 集合 元组 tuple new_tuple = tuple({1, 2, 3, 4, 5})
5、练习
综合之前的学习内容，打印一个九九乘法表（之后学习循环之后会少很多代码）
# coding:utf-8 ''' 1 * 1 = 1 2 * 1 = 2 2 * 2 = 4 3 * 1 = 3 3 * 2 = 6 3 * 3 = 9 4 * 1 = 4 4 * 2 = 8 4 * 3 = 12 4 * 4 = 16 5 * 1 = 5 5 * 2 = 10 5 * 3 = 15 5 * 4 = 20 5 * 5 = 25 6 * 1 = 6 6 * 2 = 12 6 * 3 = 18 6 * 4 = 24 6 * 5 = 30 6 * 6 = 36 7 * 1 = 7 7 * 2 = 14 7 * 3 = 21 7 * 4 = 28 7 * 5 = 35 7 * 6 = 42 7 * 7 = 49 8 * 1 = 8 8 * 2 = 16 8 * 3 = 24 8 * 4 = 32 8 * 5 = 40 8 * 6 = 48 8 * 7 = 56 8 * 8 = 64 9 * 1 = 9 9 * 2 = 18 9 * 3 = 27 9 * 4 = 36 9 * 5 = 45 9 * 6 = 54 9 * 7 = 63 9 * 8 = 72 9 * 9 = 81 ''' work = {} # 1 one_value = (1,) one_key = 1 work[str(one_key)] = one_value print(work) # 2 two_key = 2 two_value = [] two_value.append(1) two_value.append(2) work[str(two_key)] = two_value # 3 three_key = 3 three_value = [] three_value.append(1) three_value.append(2) three_value.append(3) work[str(three_key)] = three_value # 4 four_key = 4 four_value = [] four_value.append(1) four_value.append(2) four_value.append(3) four_value.append(4) work[str(four_key)] = four_value temp_five = (1, 2, 3, 4, 5) five_key = 5 five_value = [] five_value.extend(temp_five) work[str(five_key)] = five_value print(work) # 6 temp_six = [1, 2, 3, 4, 5, 6] six_key = 6 six_value = [] six_value.extend(temp_six) work[str(six_key)] = six_value # 7 temp_seven = {1, 2, 3, 4, 5, 6, 7} seven_key = 7 seven_value = [] seven_value.extend(temp_seven) work[str(seven_key)] = seven_value # 8 temp_eight = [1, 2, 3, 4, 5, 6, 7, 8] eight_key = 8 eight_value = [] eight_value.extend(temp_eight) eight_key = str(eight_key) work[eight_key] = eight_value # 9 temp_nine = (1, 2, 3, 4, 5, 6, 7, 8, 9) nine_key = 9 nine_value = list(temp_nine) nine_key = str(nine_key) work.update({nine_key: nine_value}) print(work) _keys = work.keys() keys = list(_keys) print(keys) one = keys[0] one_value = work.pop(one) print(one, one_value) one_key = int(one) print('{} * {} = {}'.format(one_key, one_value[0], one_key * one_value[0])) two = keys[1] two_value = work.pop(two) print('{} * {} = {}'.format(two, two_value[0], int(two) * two_value[0]), end=' ') print('{} * {} = {}'.format(two, two_value[1], int(two) * two_value[1])) three = keys[2] three_value = work.pop(three) print('{} * {} = {}'.format(three, three_value[0], int(three) * three_value[0]), end=' ') print('{} * {} = {}'.format(three, three_value[1], int(three) * three_value[1]), end=' ') print('{} * {} = {}'.format(three, three_value[2], int(three) * three_value[2])) four = keys[3] four_value = work.pop(four) print('{} * {} = {}'.format(four, four_value[0], int(four) * four_value[0]), end=' ') print('{} * {} = {}'.format(four, four_value[1], int(four) * four_value[1]), end=' ') print('{} * {} = {}'.format(four, four_value[2], int(four) * four_value[2]), end=' ') print('{} * {} = {}'.format(four, four_value[-1], int(four) * four_value[-1])) five = keys[4] five_value = work.pop(five) print('%s * %s = %s' % (five, five_value[0], int(five) * five_value[0]), end=' ') print('%s * %s = %s' % (five, five_value[1], int(five) * five_value[1]), end=' ') print('%s * %s = %d' % (five, five_value[2], int(five) * five_value[2]), end=' ') print('%s * %s = %d' % (five, five_value[3], int(five) * five_value[3]), end=' ') print('%s * %s = %d' % (five, five_value[-1], int(five) * five_value[-1])) six = keys[5] six_value = work.pop(six) print('%s * %s = %s' % (six, six_value[0], int(six) * six_value[0]), end=' ') print('%s * %s = %s' % (six, six_value[1], int(six) * six_value[1]), end=' ') print('%s * %s = %s' % (six, six_value[2], int(six) * six_value[2]), end=' ') print('{} * {} = {}'.format(six, six_value[3], int(six) * six_value[3]), end=' ') print('{} * {} = {}'.format(six, six_value[4], int(six) * six_value[4]), end=' ') print('{} * {} = {}'.format(six, six_value[5], int(six) * six_value[5])) seven = keys[6] seven_value = work.pop(seven) print('{} * {} = {}'.format(seven, seven_value[0], int(seven) * seven_value[0]), end=' ') print('{} * {} = {}'.format(seven, seven_value[1], int(seven) * seven_value[1]), end=' ') print('{} * {} = {}'.format(seven, seven_value[2], int(seven) * seven_value[2]), end=' ') print('{} * {} = {}'.format(seven, seven_value[3], int(seven) * seven_value[3]), end=' ') print('{} * {} = {}'.format(seven, seven_value[4], int(seven) * seven_value[4]), end=' ') print('{} * {} = {}'.format(seven, seven_value[5], int(seven) * seven_value[5]), end=' ') print('{} * {} = {}'.format(seven, seven_value[6], int(seven) * seven_value[6])) eight = keys[7] eight_value = work.pop(eight) print('{} * {} = {}'.format(eight, eight_value[0], int(eight) * eight_value[0]), end=' ') print('{} * {} = {}'.format(eight, eight_value[1], int(eight) * eight_value[1]), end=' ') print('{} * {} = {}'.format(eight, eight_value[2], int(eight) * eight_value[2]), end=' ') print('{} * {} = {}'.format(eight, eight_value[3], int(eight) * eight_value[3]), end=' ') print('{} * {} = {}'.format(eight, eight_value[4], int(eight) * eight_value[4]), end=' ') print('{} * {} = {}'.format(eight, eight_value[5], int(eight) * eight_value[5]), end=' ') print('{} * {} = {}'.format(eight, eight_value[6], int(eight) * eight_value[6]), end=' ') print('{} * {} = {}'.format(eight, eight_value[7], int(eight) * eight_value[7])) nine = keys[-1] nine_value = work.get(nine) format_str = '{} * {} = {}' print(format_str.format(nine, nine_value[0], int(nine) * nine_value[0]), end=' ') print(format_str.format(nine, nine_value[1], int(nine) * nine_value[1]), end=' ') print(format_str.format(nine, nine_value[2], int(nine) * nine_value[2]), end=' ') print(format_str.format(nine, nine_value[3], int(nine) * nine_value[3]), end=' ') print(format_str.format(nine, nine_value[4], int(nine) * nine_value[4]), end=' ') print(format_str.format(nine, nine_value[5], int(nine) * nine_value[5]), end=' ') print(format_str.format(nine, nine_value[6], int(nine) * nine_value[6]), end=' ') print(format_str.format(nine, nine_value[7], int(nine) * nine_value[7]), end=' ') print(format_str.format(nine, nine_value[-1], int(nine) * nine_value[-1]))
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