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一、变量在python中不需要为变量制定数据类型。可以单行定义多个变量。
>>> a, b = 2, 3.4 >>> a 2 >>> type(a) <class 'int'> >>> type(b) <class 'float'> >>> b 3.4
还可以这样进行解压赋值,前提是变量的数量必须跟序列或元组的元素数量一样,
>>> date = ('Forsk', 'China', 'Python') >>> name, country, language = date >>> name 'Forsk' >>> country 'China' >>> language 'Python' >>>
>>> data = ['Forsk', (2018, 1, 11)] >>> name, time = data >>> name 'Forsk' >>> time (2018, 1, 11) >>> name, (year, mon, day) = data >>> name 'Forsk' >>> year 2018 >>> mon 1 >>> day 11
若变量的数量和元素数量不一致,将产生一个异常,
>>> name, (year, mon) = data Traceback (most recent call last): File "<stdin>", line 1, in <module> ValueError: too many values to unpack (expected 2)
如果只想要解压其中一部分的值,丢弃其他,可以这样做,
>>> _, (year, mon, day) = data >>> year 2018 >>> mon 1 >>> day 11
然后丢弃_就可以了。
如果元素数量太多时,我们不可能给每个元素都分配一个变量,可以这样
>>> record = ('Forsk', 'forskwill@gmail.com', '13131313131', '6676-6666') >>> name, email, *phone_number = record >>> name 'Forsk' >>> email 'forskwill@gmail.com' >>> phone_number ['13131313131', '6676-6666']
使用*解压之后得到的变量永远是列表类型,不需要做类型检查。
如果我们想得到头尾的值,可以这样
>>> name, *information, phone_number = record >>> name 'Forsk' >>> phone_number '6676-6666'
从键盘获取输入
python3中使用input()
二、运算符和表达式
可在python界面直接使用运算符操作
>>> 2 + 3 5 >>> 5 - 6 -1 >>> 2 * 3 6 >>> 4 / 3 1.3333333333333333 >>> 4 % 3 1 >>> 5 % 3 2
关系运算符和逻辑运算符
< Is less than
<= Is less than or equal to
> Is greater than
>= Is greater than or equal to
== Is equal to
!= Is not equal to
>>> 1 < 2 True >>> 3 < 2 False >>> True or False True >>> True and False False >>> not True False >>> not False True
运算符的简写
>>> a = 2 >>> a += 3 >>> a 5
运算符表达式符合正常数学逻辑
>>> a = 9 >>> b = 12 >>> c = 3 >>> x = a - b / 3 + c * 2 - 1 >>> x 10.0
('/'除以得到是float)
三、类型转换
float(string)
int(string)
str(integer)
str(float)
标签:lin less .com 检查 traceback pytho recent 产生 form
原文地址:http://blog.51cto.com/forsk/2059900