1. 数据类型
2. 基础数据类型
2.1. 前提条件
python 基本环境已经安装并配置成功,可以在任意目录中运行 python 脚本命令.
$ python
WARNING: Python 2.7 is not recommended.
This version is included in macOS for compatibility with legacy software.
Future versions of macOS will not include Python 2.7.
Instead, it is recommended that you transition to using 'python3' from within Terminal.
Python 2.7.16 (default, Nov 9 2019, 05:55:08)
[GCC 4.2.1 Compatible Apple LLVM 11.0.0 (clang-1100.0.32.4) (-macos10.15-objc-s on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>
macOS系统默认自带python环境,然而版本较低,一般都是python2,目前主流软件一般使用python3,所以需要自行安装python3.
根据命令行输出内容提示 python 命令默认使用的是 python2.7 版本,推荐使用 python3 命令,这里默认读者已经安装并配置好 python3 的相关环境.
不论输入 python 还是 python3 命令,只要出现 >>> 提示符即表示已经进入 python 环境,下面可以直接运行 python 脚本.
Python 2.7.16 (default, Nov 9 2019, 05:55:08)
[GCC 4.2.1 Compatible Apple LLVM 11.0.0 (clang-1100.0.32.4) (-macos10.15-objc-s on darwin
Type "help", "copyright", "credits" or "license" for more information.
- 帮助命令
在 python 命令行环境中,根据上一步的提示可以输入 Type "help", "copyright", "credits" or "license" for more information. 获取更多信息,按照提示输入 help 命令得到下面的输出内容:
>>> help
Type help() for interactive help, or help(object) for help about object.
根据提示应该输入 help() 获取交互性帮助或者输入 help(object) 获取关于对象的帮助信息.
如你提示,让我们继续尝试,看一下会输出什么样的帮助信息:
>>> help()
Welcome to Python 2.7! This is the online help utility.
If this is your first time using Python, you should definitely check out
the tutorial on the Internet at http://docs.python.org/2.7/tutorial/.
Enter the name of any module, keyword, or topic to get help on writing
Python programs and using Python modules. To quit this help utility and
return to the interpreter, just type "quit".
To get a list of available modules, keywords, or topics, type "modules",
"keywords", or "topics". Each module also comes with a one-line summary
of what it does; to list the modules whose summaries contain a given word
such as "spam", type "modules spam".
help>
由此可见,确实输出了一大堆帮助信息,这是在线帮助工具,如果是新手,推荐阅读在线教程
在使用中遇到不懂的地方可以获取帮助文档,如需退出帮助文档可以输入 quit 命令.
比如想要获取可用模块,关键字,主题等,可以输入 modules ,keywords ,topics ,同时还会继续给出详细帮助信息,比如现在可以输入 modules spam 查看关于 spam 模块的帮助信息.
注意: 从最初的
python交互式命令行中输入help()已经进入了帮助文档的交互式命令环境,最左边的命令行提示符也由>>>变成了现在的help>,表明两者不是一个环境!
help> modules spam
Here is a list of matching modules. Enter any module name to get more help.
在帮助文档交互环境中输入
modules spam命令可以获取相关的帮助信息,具体的帮助信息因命令不同而不同,不再深究.
现在如果想要退回帮助文档交互式环境返回到 python 命令交互式环境的话,只需要按照输入 help() 命令给出的提示信息输入 quit 即可返回继续输入其余的 "help", "copyright", "credits" or "license" 等命令.
help> quit
You are now leaving help and returning to the Python interpreter.
If you want to ask for help on a particular object directly from the
interpreter, you can type "help(object)". Executing "help('string')"
has the same effect as typing a particular string at the help> prompt.
>>>
命令提示符已经从 help> 变回了 >>> ,表明现在已经离开了帮助环境并进入 python 环境.
- 版权命令
尝试过 help() 命令后,继续一次尝试其余的几个命令: Type "help", "copyright", "credits" or "license" for more information.
>>> copyright
Copyright (c) 2001-2019 Python Software Foundation.
All Rights Reserved.
Copyright (c) 2000 BeOpen.com.
All Rights Reserved.
Copyright (c) 1995-2001 Corporation for National Research Initiatives.
All Rights Reserved.
Copyright (c) 1991-1995 Stichting Mathematisch Centrum, Amsterdam.
All Rights Reserved.
>>>
copyright命令直接输出了版权信息,最左边的命令行提示符并没有发生改变,表明现在依然是处于python交互式环境.
- 致谢人员
依然处于 python 交互式环境中输入 credits 命令可以查看 python 的幕后工作人员,也可以访问www.python.org 查看更多信息.
>>> credits
Thanks to CWI, CNRI, BeOpen.com, Zope Corporation and a cast of thousands
for supporting Python development. See www.python.org for more information.
>>>
Python的发展壮大离不开贡献者的辛苦付出,感谢大佬们的智慧.
- 版权命令
现在只剩下最后一个 license 命令,已经迫不及待想要快点结束了!
>>> license
Type license() to see the full license text
看样子和 help 命令一样,不是直接输入 license 而是需要输入 license() 命令才可以查看版权信息,难不成还会离开 >>> 提示符的 python 环境吗?
>>> license()
A. HISTORY OF THE SOFTWARE
==========================
Python was created in the early 1990s by Guido van Rossum at Stichting
Mathematisch Centrum (CWI, see http://www.cwi.nl) in the Netherlands
as a successor of a language called ABC. Guido remains Python's
principal author, although it includes many contributions from others.
In 1995, Guido continued his work on Python at the Corporation for
National Research Initiatives (CNRI, see http://www.cnri.reston.va.us)
in Reston, Virginia where he released several versions of the
software.
In May 2000, Guido and the Python core development team moved to
BeOpen.com to form the BeOpen PythonLabs team. In October of the same
year, the PythonLabs team moved to Digital Creations, which became
Zope Corporation. In 2001, the Python Software Foundation (PSF, see
https://www.python.org/psf/) was formed, a non-profit organization
created specifically to own Python-related Intellectual Property.
Zope Corporation was a sponsoring member of the PSF.
All Python releases are Open Source (see http://www.opensource.org for
the Open Source Definition). Historically, most, but not all, Python
Hit Return for more, or q (and Return) to quit:
命令行提示符好像没有发生变化,最后一句话说想要查看更多信息可以敲入 回车 键或者输入 q (然后 回车) 退出.
releases have also been GPL-compatible; the table below summarizes
the various releases.
Release Derived Year Owner GPL-
from compatible? (1)
0.9.0 thru 1.2 1991-1995 CWI yes
1.3 thru 1.5.2 1.2 1995-1999 CNRI yes
1.6 1.5.2 2000 CNRI no
2.0 1.6 2000 BeOpen.com no
1.6.1 1.6 2001 CNRI yes (2)
2.1 2.0+1.6.1 2001 PSF no
2.0.1 2.0+1.6.1 2001 PSF yes
2.1.1 2.1+2.0.1 2001 PSF yes
2.1.2 2.1.1 2002 PSF yes
2.1.3 2.1.2 2002 PSF yes
2.2 and above 2.1.1 2001-now PSF yes
Footnotes:
(1) GPL-compatible doesn't mean that we're distributing Python under
the GPL. All Python licenses, unlike the GPL, let you distribute
a modified version without making your changes open source. The
Hit Return for more, or q (and Return) to quit:
显示了更多的信息,最后一句话依然是 "Hit Return for more, or q (and Return) to quit: " ,这一次当然是 q 并回车了啊!
Hit Return for more, or q (and Return) to quit: q
>>>
再一次出现 >>> 提示符,现在可以继续愉快地玩耍 python 脚本了呢!
2.2. 你好,python
如果还没有进入 python 环境,可以输入 python 或者 python3 进入交互式环境.
$ python
WARNING: Python 2.7 is not recommended.
This version is included in macOS for compatibility with legacy software.
Future versions of macOS will not include Python 2.7.
Instead, it is recommended that you transition to using 'python3' from within Terminal.
Python 2.7.16 (default, Nov 9 2019, 05:55:08)
[GCC 4.2.1 Compatible Apple LLVM 11.0.0 (clang-1100.0.32.4) (-macos10.15-objc-s on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>
如果是
python2环境可以输入python进入交互式环境.
$ python3
Python 3.7.5 (default, Nov 1 2019, 02:16:23)
[Clang 11.0.0 (clang-1100.0.33.8)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>
如果是
python3环境可以输入python3进入交互式环境.
如果你正在处于 python 交互式环境,可以输入 print('hello python!') 来表明正式入门开始学习 python .
>>> print('hello python!')
hello python!
如果你想退出 python 环境可以输入 exit() 命令或者 Ctrl-D 来退出.
>>> exit
Use exit() or Ctrl-D (i.e. EOF) to exit
>>> exit()
$
按照已有的开发经验推断,退出命令行可以输入
quit或exit或者Ctrl-D,试错学习后知道了想要退出python环境支持exit() or Ctrl-D两种方式.
2.3. 扫盲基本类型
2.3.1. 整数
和其他编程语言一样,整数和数学意义上的概念一样,在 python 交互式命令行环境中支持四则运算,请不要问 5/2 为什么等于 2 而不是 2.5 这样的基础问题.
>>> 1
1
>>> 1+1
2
2.3.2. 小数
不同于整数之处在于浮点数保留小数,整数运算的 5/2=2 而浮点数运算的 5.0/2 或者 5/2.0 均等于 2.5 而不是 2 .
>>> 3.1415926*2
6.2831852
>>> 5/2.0
2.5
>>> 5.0/2
2.5
>>>
当数据非常大或者非常小的时候,浮点数可以用来表示科学计算法,比如先定一个小目标,一年挣他一个亿?
>>> 1.0e8
100000000.0
>>> 1e8
100000000.0
>>> 1e-2
0.01
不论是
1.0e8还是1e8计算结果均是浮点数,不信你自己试试看!
2.3.3. 字符串
不论是现实生活中还是计算机的编程世界里,字符串才是使用最频繁的一种数据类型,python 中的字符串和数字类型在一起会发生什么样的关系呢?
- 左右单引号和双引号均可,但不支持混用
左边包裹的是双引号
",则右边也必须是双引号",如果左边是单引号'则右边也需要是单引号'.
>>> print("hello python!")
hello python!
>>> print('hello python!')
hello python!
正确示例:
print("hello python!")或print('hello python!')
>>> print("hello python!')
File "<stdin>", line 1
print("hello python!')
^
SyntaxError: EOL while scanning string literal
>>> print('hello python!")
File "<stdin>", line 1
print('hello python!")
^
SyntaxError: EOL while scanning string literal
错误示例:
print("hello python!')或print('hello python!")
- 内部单引号和双引号可配合,特殊字符要转义
如果用单引号包裹字符串而该字符串本身也有单引号,则需要使用
\'进行转义('welcome to \'snowdreams1006.cn\''),如果该字符串是双引号,那么可以直接使用('welcome to "snowdreams1006.cn"'). 如果用双引号包裹的字符串也是类似情况,分别是"welcome to \"snowdreams1006.cn\""和"welcome to 'snowdreams1006.cn'".
>>> print("welcome to snowdreams1006.cn")
>>> print('welcome to snowdreams1006.cn')
>>> print("welcome to 'snowdreams1006.cn'")
welcome to 'snowdreams1006.cn'
>>> print('welcome to "snowdreams1006.cn"')
welcome to "snowdreams1006.cn"
>>> print('welcome to \'snowdreams1006.cn\'')
welcome to 'snowdreams1006.cn'
>>> print("welcome to \"snowdreams1006.cn\"")
welcome to "snowdreams1006.cn"
正确示例:
print("welcome to 'snowdreams1006.cn'")或print('welcome to "snowdreams1006.cn"')或print('welcome to \'snowdreams1006.cn\'')或print("welcome to \"snowdreams1006.cn\"")
>>> print("welcome to "snowdreams1006.cn"")
File "<stdin>", line 1
print("welcome to "snowdreams1006.cn"")
^
SyntaxError: invalid syntax
>>> print('welcome to 'snowdreams1006.cn'')
File "<stdin>", line 1
print('welcome to 'snowdreams1006.cn'')
^
SyntaxError: invalid syntax
错误示例:
print("welcome to "snowdreams1006.cn"")或print('welcome to 'snowdreams1006.cn'')
- 多行字符串可换行可注释
如果你是在 python 交互式命令行环境中输入多行字符串,可以先输入 print(''' 然后按下回车出现... 等待继续输入 welcome to snowdreams1006.cn ,输入完成后再次回车换行接着输入 or ,再次回车换行直到输入 ''') 回车完成!
>>> print('''
... welcome to snowdreams1006.cn
... or
... you can visit on snowdreams1006.tech
... ''')
welcome to snowdreams1006.cn
or
you can visit on snowdreams1006.tech
如果是直接复制多行命令的话,可以使用三个连续单引号或双引号分割多行字符串,复制到 python 交互式命令行中直接体验.
print('''
welcome to snowdreams1006.cn
or
you can visit on snowdreams1006.tech
''')
print("""
welcome to snowdreams1006.cn
or
you can visit on snowdreams1006.tech
""")
最终输出结果就是多行字符串原样展示,支持换行!
welcome to snowdreams1006.cn
or
you can visit on snowdreams1006.tech
连续字符串不仅可以用于处理换行字符串还可以用作注释,比如 python 文件内容如下:
'''
my wechat is snowdreams1006
'''
"""
my wechat is snowdreams1006
"""
print('''
welcome to snowdreams1006.cn
or
you can visit on snowdreams1006.tech
''')
# python is the best language in the world
test.py文件中,以#开头的字符串不会执行,表示单行注释,以'''开头并且以'''结尾的表示多行注释.
当我们处于正常的命令行模式下直接运行该脚本文件,我们会发现多行注释和单行注释均不会执行输出!
$ python test.py
welcome to snowdreams1006.cn
or
you can visit on snowdreams1006.tech
注意: 这里执行
python脚本文件的命令行不是python交互式命令行环境而是普通的正常模式,请注意命令行提示符的区别!
- 数字遇到字符串会报错
>>> 1+1
2
>>> '1'+'1'
'11'
正确示例: 数字和数字之间
+表示数学意义上的加法即1+1结果是2,而字符串之间的+表示连接符即'1'+'1'的结果是'11'.
>>> 1+'1'
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for +: 'int' and 'str'
>>> '1'+1
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: cannot concatenate 'str' and 'int' objects
>>>
错误示例: 数字和字符串直接使用
+会报错,不论是1+'1'还是'1'+1均不支持!
2.3.4. 相互转换
- 其他类型转字符串
str()函数将其他类型转字符串,包括类整数字符串转字符串,类小数字符串转字符串,整数转字符串和小数转字符串.
>>> str('1')
'1'
>>> str('1.9')
'1.9'
>>> str(1)
'1'
>>> str(1.9)
'1.9'
因此我们可以使用 str() 完成字符串拼接的需求,不用再担心 1+'1' 会报错了,只需要这么处理:
>>> str(1) + str('1')
'11'
- 其他类型转小数
float()函数可以将其他类型转小数,包括小数转小数,整数转小数,类小数的字符串转小数,类整数的字符串转小数.
>>> float(1)
1.0
>>> float(1.9)
1.9
>>> float('1')
1.0
>>> float('1.9')
1.9
- 其他类型转整数
int()函数可以将其他类型转整数,包括整数转整数,小数转整数,类整数字符串转整数,但不支持类小数字符串转整数!
>>> int(1)
1
>>> int(1.9)
1
>>> int(10.9)
10
>>> int('1')
1
>>> int('1.9')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: invalid literal for int() with base 10: '1.9'
>>>
由于 int() 函数有坑,因此遇到类小数字符串转换成整数时需要特殊处理,可以先用 float() 函数将类小数字符串转成小数,再用 int() 函数将刚才的小数转成整数.
>>> int(float('1.9'))
1
2.4. 学习总结
本文主要介绍了 python 环境安装完毕后如何进入命令行交互式环境以及运行 Hello World,然后学习了 python 的基本数据类型以及相互转换.
str()其他类型转字符串,放心使用,无论是整数还是小数或者原本就是字符串都能转成字符串.
>>> print(str('welcome to "snowdreams')+str(1006)+str(".cn\""))
welcome to "snowdreams1006.cn"
float()其他类型转小数,正常使用,无论是整数还是小数或者类小数字符串或类整数字符串都能转成小数.
>>> print(float('1006')+float('10.06')+float(10)+float(.06))
1026.12
int()其他类型转整数,小心使用,整数和小数以及类整数字符串可以转成整数,其中小数部分会直接舍弃,不支持类小数字符串!
>>> print(int('1006')+int(float('10.06'))+int(10)+int(.06))
1026
当然还有一种显而易见的情况,不是数字类型的字符串任 float() 还是 int() 怎么折腾也是无能为力的,奇技淫巧除外!
>>> print(float('welcome to "snowdreams1006.cn"'))
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: could not convert string to float: welcome to "snowdreams1006.cn"
>>> print(int('welcome to "snowdreams1006.cn"'))
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: invalid literal for int() with base 10: 'welcome to "snowdreams1006.cn"'
2.5. 阅读更多
作者: 雪之梦技术驿站
链接: https://snowdreams1006.github.io/learn-python/quickstart/type.html
来源: 雪之梦技术驿站
本文原创发布于「雪之梦技术驿站」,转载请注明出处,谢谢合作!
