python 关键知识点

学习资源：笨方法学习 python3

将变量传递给脚本——argv

• 脚本：你编写的 .py 文件。
• argv 参数变量（argument variable）保存着你运行 python 脚本的参数。

input() 脚本运行过程需要输入参数

from sys import argv

script, user_name = argv  # 解包
prompt = '> '    # 提示符

print(f"Hi {user_name}, I'm the {script} script.")
print("I'd like to ask you a few question.")
print(f"Do you like me {user_name}?")
likes = input(prompt)

print(f"Where do you live {user_name}?")
lives = input(prompt)

print("What kind of computer do you have?")
computer = input(prompt)

print(f'''
Alright, so you said {likes} about liking me.
You live in {lives}. Not sure where that is.
And you have a {computer} computer. Nice.
''')

x = input('sd ffg')

sd ffgdf

type(x)

str

x

'df'

echo 'This is a text file.' > a.txt   # 创建文件 

cat a.txt    # 查看文件

man cat   # 查看 cat 的帮助文档

函数中的 *args

告诉 python 把函数的所有参数都接收进来，然后放到名叫 args 的列表中去。

def print_two(*args):
    arg1, arg2 = args
    print(f'arg1: {arg1}, arg2: {arg2}')

print_two('Zed', 'Shaw')

arg1: Zed, arg2: Shaw

字符串 & 字节串 & 字符编码

import sys

script, encoding, error = sys.argv

def main(language_file, encoding, errors):
    line = language_file.readline()
    if line:
        print_line(line, encoding, errors)
        return main(language_file, encoding, errors)

def print_line(line, encoding, errors):
    next_lang = line.strip()
    raw_bytes = next_lang.encode(encoding, errors = errors)
    cooked_string = raw_bytes.decode(encoding, errors = errors)
    
    print(raw_bytes, "<===>", cooked_string)

languages = open('E:/Data/languages.txt', encoding = 'utf-8')

main(languages, encoding, error)

PowerShell：

python .str_bytes_test.py utf-8 strict

def main(language_file, encoding, errors):
    line = language_file.readline()
    if line:
        print_line(line, encoding, errors)
        return main(language_file, encoding, errors)

def print_line(line, encoding, errors):
    next_lang = line.strip()     # 删除每行结尾的 "
"
    raw_bytes = next_lang.encode(encoding, errors = errors)
    cooked_string = raw_bytes.decode(encoding, errors = errors)

    print(raw_bytes, "<===>", cooked_string)

with open('E:/Data/languages.txt', encoding = 'utf-8') as fp:
    main(fp, 'utf-8', 'strict')

b'Afrikaans' <===> Afrikaans
b'xe1x8axa0xe1x88x9bxe1x88xadxe1x8ax9b' <===> አማርኛ
b'xd0x90xd2xa7xd1x81xd1x88xd3x99xd0xb0' <===> Аҧсшәа
b'xd8xa7xd9x84xd8xb9xd8xb1xd8xa8xd9x8axd8xa9' <===> العربية
b'Aragonxc3xa9s' <===> Aragonés
b'Arpetan' <===> Arpetan
b'Azxc9x99rbaycanca' <===> Azərbaycanca
b'Bamanankan' <===> Bamanankan
b'xe0xa6xacxe0xa6xbexe0xa6x82xe0xa6xb2xe0xa6xbe' <===> বাংলা
b'Bxc3xa2n-lxc3xa2m-gxc3xba' <===> Bân-lâm-gú
b'xd0x91xd0xb5xd0xbbxd0xb0xd1x80xd1x83xd1x81xd0xbaxd0xb0xd1x8f' <===> Беларуская
b'xd0x91xd1x8axd0xbbxd0xb3xd0xb0xd1x80xd1x81xd0xbaxd0xb8' <===> Български
b'Boarisch' <===> Boarisch
b'Bosanski' <===> Bosanski
b'xd0x91xd1x83xd1x80xd1x8fxd0xb0xd0xb4' <===> Буряад
b'Catalxc3xa0' <===> Català
b'xd0xa7xd3x91xd0xb2xd0xb0xd1x88xd0xbbxd0xb0' <===> Чӑвашла
b'xc4x8cexc5xa1tina' <===> Čeština
b'Cymraeg' <===> Cymraeg
b'Dansk' <===> Dansk
b'Deutsch' <===> Deutsch
b'Eesti' <===> Eesti
b'xcex95xcexbbxcexbbxcexb7xcexbdxcexb9xcexbaxcexac' <===> Ελληνικά
b'Espaxc3xb1ol' <===> Español
b'Esperanto' <===> Esperanto
b'xd9x81xd8xa7xd8xb1xd8xb3xdbx8c' <===> فارسی
b'Franxc3xa7ais' <===> Français
b'Frysk' <===> Frysk
b'Gaelg' <===> Gaelg
b'Gxc3xa0idhlig' <===> Gàidhlig
b'Galego' <===> Galego
b'xedx95x9cxeaxb5xadxecx96xb4' <===> 한국어
b'xd5x80xd5xa1xd5xb5xd5xa5xd6x80xd5xa5xd5xb6' <===> Հայերեն
b'xe0xa4xb9xe0xa4xbfxe0xa4xa8xe0xa5x8dxe0xa4xa6xe0xa5x80' <===> हिन्दी
b'Hrvatski' <===> Hrvatski
b'Ido' <===> Ido
b'Interlingua' <===> Interlingua
b'Italiano' <===> Italiano
b'xd7xa2xd7x91xd7xa8xd7x99xd7xaa' <===> עברית
b'xe0xb2x95xe0xb2xa8xe0xb3x8dxe0xb2xa8xe0xb2xa1' <===> ಕನ್ನಡ
b'Kapampangan' <===> Kapampangan
b'xe1x83xa5xe1x83x90xe1x83xa0xe1x83x97xe1x83xa3xe1x83x9axe1x83x98' <===> ქართული
b'xd2x9axd0xb0xd0xb7xd0xb0xd2x9bxd1x88xd0xb0' <===> Қазақша
b'Kreyxc3xb2l ayisyen' <===> Kreyòl ayisyen
b'Latgaxc4xbcu' <===> Latgaļu
b'Latina' <===> Latina
b'Latviexc5xa1u' <===> Latviešu
b'Lxc3xabtzebuergesch' <===> Lëtzebuergesch
b'Lietuvixc5xb3' <===> Lietuvių
b'Magyar' <===> Magyar
b'xd0x9cxd0xb0xd0xbaxd0xb5xd0xb4xd0xbexd0xbdxd1x81xd0xbaxd0xb8' <===> Македонски
b'Malti' <===> Malti
b'xe0xa4xaexe0xa4xb0xe0xa4xbexe0xa4xa0xe0xa5x80' <===> मराठी
b'xe1x83x9bxe1x83x90xe1x83xa0xe1x83x92xe1x83x90xe1x83x9axe1x83xa3xe1x83xa0xe1x83x98' <===> მარგალური
b'xd9x85xd8xa7xd8xb2xd9x90xd8xb1xd9x88xd9x86xdbx8c' <===> مازِرونی
b'Bahasa Melayu' <===> Bahasa Melayu
b'xd0x9cxd0xbexd0xbdxd0xb3xd0xbexd0xbb' <===> Монгол
b'Nederlands' <===> Nederlands
b'xe0xa4xa8xe0xa5x87xe0xa4xaaxe0xa4xbexe0xa4xb2 xe0xa4xadxe0xa4xbexe0xa4xb7xe0xa4xbe' <===> नेपाल भाषा
b'xe6x97xa5xe6x9cxacxe8xaax9e' <===> 日本語
b'Norsk bokmxc3xa5l' <===> Norsk bokmål
b'Nouormand' <===> Nouormand
b'Occitan' <===> Occitan
b'Oxcaxbbzbekcha/xd1x9exd0xb7xd0xb1xd0xb5xd0xbaxd1x87xd0xb0' <===> Oʻzbekcha/ўзбекча
b'xe0xa8xaaxe0xa9xb0xe0xa8x9cxe0xa8xbexe0xa8xacxe0xa9x80' <===> ਪੰਜਾਬੀ
b'xd9xbexd9x86xd8xacxd8xa7xd8xa8xdbx8c' <===> پنجابی
b'xd9xbexdax9axd8xaaxd9x88' <===> پښتو
b'Plattdxc3xbcxc3xbctsch' <===> Plattdüütsch
b'Polski' <===> Polski
b'Portuguxc3xaas' <===> Português
b'Romxc3xa2nxc4x83' <===> Română
b'Romani' <===> Romani
b'xd0xa0xd1x83xd1x81xd1x81xd0xbaxd0xb8xd0xb9' <===> Русский
b'Seeltersk' <===> Seeltersk
b'Shqip' <===> Shqip
b'Simple English' <===> Simple English
b'Slovenxc4x8dina' <===> Slovenčina
b'xdaxa9xd9x88xd8xb1xd8xafxdbx8cxdbx8c xd9x86xd8xa7xd9x88xdbx95xd9x86xd8xafxdbx8c' <===> کوردیی ناوەندی
b'xd0xa1xd1x80xd0xbfxd1x81xd0xbaxd0xb8 / srpski' <===> Српски / srpski
b'Suomi' <===> Suomi
b'Svenska' <===> Svenska
b'Tagalog' <===> Tagalog
b'xe0xaexa4xe0xaexaexe0xaexbfxe0xaexb4xe0xafx8d' <===> தமிழ்
b'xe0xb8xa0xe0xb8xb2xe0xb8xa9xe0xb8xb2xe0xb9x84xe0xb8x97xe0xb8xa2' <===> ภาษาไทย
b'Taqbaylit' <===> Taqbaylit
b'xd0xa2xd0xb0xd1x82xd0xb0xd1x80xd1x87xd0xb0/tatarxc3xa7a' <===> Татарча/tatarça
b'xe0xb0xa4xe0xb1x86xe0xb0xb2xe0xb1x81xe0xb0x97xe0xb1x81' <===> తెలుగు
b'xd0xa2xd0xbexd2xb7xd0xb8xd0xbaxd3xa3' <===> Тоҷикӣ
b'Txc3xbcrkxc3xa7e' <===> Türkçe
b'xd0xa3xd0xbaxd1x80xd0xb0xd1x97xd0xbdxd1x81xd1x8cxd0xbaxd0xb0' <===> Українська
b'xd8xa7xd8xb1xd8xafxd9x88' <===> اردو
b'Tixe1xbaxbfng Vixe1xbbx87t' <===> Tiếng Việt
b'Vxc3xb5ro' <===> Võro
b'xe6x96x87xe8xa8x80' <===> 文言
b'xe5x90xb4xe8xafxad' <===> 吴语
b'xd7x99xd7x99xd6xb4xd7x93xd7x99xd7xa9' <===> ייִדיש
b'xe4xb8xadxe6x96x87' <===> 中文

现代的计算机本质上是一个巨大的开关阵列。计算机用电来触发这些开关的开启或关闭。这些开关用 1 表示开启、有电、接通，用 0 表示关闭、没电、切断。我们称这些 1 和 0 为『位』（bit）。

我们用「字节」（byte）表示一个 (8) 位（0 和 1）的序列。

美国信息交换标准代码（ASCII）把数字与字母相对应。

0b1011010   # 二进制的 90

90

ord('Z')  # 字母 Z 的对应数字

90

chr(90) 

'Z'

有了 ASCII 这个约定，我们就可以用 (8) 位（也就是 (1) 字节）编码一个字符，然后就可以把字符串联在一起，合成一个单词。例如：'Zed A. Shaw' 我们可以用一组字节序列来表示：[90, 101, 100, 32, 65, 46, 32, 83, 104, 97, 119]，代码如下：

[ord(name) for name in 'Zed A. Shaw']

[90, 101, 100, 32, 65, 46, 32, 83, 104, 97, 119]

再说一遍，类似上面的约定的序列最终还是会转换为开关的通断。

一个字节可以存放 (256)（即 (2 ^ 8)）个数字：

[0 sim 255 ; ext{或} ; 00000000 sim 11111111 ]

为了统一编码方式，Unicode（universal encoding）便出现了。

UTF-8（Unicode Transformation Format 8 Bits）：把大部分常用的字符用 (8) 位编码，如果需要编码更多的字符，就「逃」去使用更大的数；这种编码方式很大的程度节省了存储空间。

在 python 中，string 是 UTF-8 编码的字符序列，是显示和处理文本的基础。bytes 则是 python 用来存储 UTF-8 字符串的原始字节序列，使用b"" 表示字节串。

因而，如果要处理的是原始字节串（bytes），那么你就需要通过 .decode() 来获取字符串（string）。原始字节串不包含编码方式，它们就是字节序列，一堆数字而已，所以你必须告诉 python 把它解码成 UTF 字符串。即

解码字节串，编码字符串
（decode bytes, encode strings）

短路逻辑

• 任何以 False 开头的 and 语句都会直接处理成 False，不会继续检查后面的语句。
• 任何包含 True 的 or 语句，只要处理到 True，就不会继续向下推算，而是直接返回 True 了。
• Python 只会运行它遇到的是 True 的第一个块，所以如果有多个 elif 块，只有第一个为 True 的块才会运行。

from sys import exit

def glod_room():
    print("This room is full of gold. How much do you take?")
    
    choice = input('> ')
    if '0' in choice or '1' in choice:
        how_much = int(choice)
    else:
        dead("Man, learn to type a number.")
        
    if how_much < 50:
        print("Nice, you're not greedy, you win!")
        exit(0)
    else:
        dead("You greedy bastard!")
        

def dead(why):
    print(why, "Good Job!")
    exit(0)

glod_room()

This room is full of gold. How much do you take?
> 7
Man, learn to type a number. Good Job!



An exception has occurred, use %tb to see the full traceback.


SystemExit: 0



C:ProgramDataAnaconda3libsite-packagesIPythoncoreinteractiveshell.py:2971: UserWarning: To exit: use 'exit', 'quit', or Ctrl-D.
  warn("To exit: use 'exit', 'quit', or Ctrl-D.", stacklevel=1)

exit(0) 可以中止某个程序，而其中的数字参数用来表示程序是否是遇到错误而中止的。exit(0) 表示程序正常退出。

if 语句的规则

1. 每一条 if 语句必须包含一个 else。（为了防止出现未考虑到的条件出现）
2. 若这个 else 永远都不应该被执行到，因为它本身没有任何意义，则必须在 else 语句后面使用一个叫 die 的函数，让它打印出出错消息并且「死」给你看。
3. if 语句的嵌套不要超过两层，最好尽量保持只有一层。
4. 将 if 语句当作段落来对待，其中的每一个 if-elif-else 组合就跟一个段落的句子组合一样。在这种组合的最前面和最后面留一个空行以作区分。
5. 你的布尔测试应该很简单，如果它们很复杂，你需要在函数里面将它们的运算顺序事先放到一个变量里，并且为变量取一个名字。

调试小技巧

• 最好的调试方法是使用 print 在各个要检查的关键点将变量打印出来，从而检查那里是否有错。
• 让程序一部分一部分地运行起来。不要等到写了一大堆代码文件后才去运行它们，写一点，运行一点，再修改一点。

.join() & .split()

ten_things = 'Apples Oranges Crows Telephone Light Sugar'
stuff = ten_things.split(' ')
stuff

['Apples', 'Oranges', 'Crows', 'Telephone', 'Light', 'Sugar']

' & '.join(stuff)

'Apples & Oranges & Crows & Telephone & Light & Sugar'

面向对象（OOP）

练习：

import random
from urllib.request import urlopen
import sys

WORD_URL = 'http://learncodethehardway.org/words.txt'
WORDS = []

PHRASES = {
    'class %%%(%%%):':
    "Make a class named %%% that is-a %%%.",
    'class %%%(object):
	def __init__(self, ***)':
    'class %%% has-a __init__ that takes self and *** params.',
    'class %%%(object):
	def ***(self, @@@)':
    'class %%% has-a function *** that takes self ang @@@ params.',
    '*** = %%%()':
    'Set *** to an instance of class %%%',
    "***.***(@@@)":
    'From *** get *** function, call it with params self, @@@.',
    "***.*** = '***'":
    "From *** get the attribute and set it to '***'."
    
}

# do they want to drill phrases（短语） first
if len(sys.argv) == 2 and sys.argv[1] == 'english':
    PHRASES_FIRST = True
else:
    PHRASES_FIRST = False
    
# load up the words from website
for word in urlopen(WORD_URL).readlines():
    WORDS.append(str(word.strip(), encoding = 'utf-8'))
    

def convert(snippet, phrase):
    class_names = [w.capitalize() for w in random.sample(WORDS, snippet.count("%%%"))]
    other_names = random.sample(WORDS, snippet.count("***"))
    results = []
    param_names = []
    
    for i in range(0, snippet.count('@@@')):
        param_count = random.randint(1, 3)
        param_names.append(', '.join(random.sample(WORDS, param_count)))
        
    for sentence in snippet, phrase:
        result = sentence[:]
        
        # fake class names
        for word in class_names:
            result = result.replace("%%%", word, 1)
            
        # fake other names
        for word in other_names:
            result = result.replace("***", word, 1)
            
        # fake parameter lists
        for word in param_names:
            result = result.replace("@@@", word, 1)
            
        results.append(result)
        
    return results


# keep going until they hit CTRAL-D
try:
    while True:
        snippets = list(PHRASES.keys())
        random.shuffle(snippets)
        
        for snippet in snippets:
            phrase = PHRASES[snippet]
            question, answer = convert(snippet, phrase)
            if PHRASES_FIRST:
                question, answer = question, answer
            
            print(question)
            
            input("> ")
            print(f"ANSWER: {answer}

")
except EOFError:
    print('
Bye')

关于 class Name(object)

在 python 3 中，你不需要在类名后面添加 object，但是 python 圈子的人相信「显式优于隐式」，所以，一般还是需要写上。

关于 super()

在 python 3 中 super() 等价于 super(Child, self)

class Parent(object):
    
    def altered(self):
        print("PARENT altered()")
        
class Child(Parent):
    
    def altered(self):
        print("CHILD, BEFORE PARENT altered()")
        super(Child, self).altered()
        print("CHILD, AFTER PARENT altered()")
        
dad = Parent()
son = Child()

dad.altered()
print('=='* 20)
son.altered()

PARENT altered()
========================================
CHILD, BEFORE PARENT altered()
PARENT altered()
CHILD, AFTER PARENT altered()

class Parent(object):
    
    def altered(self):
        print("PARENT altered()")
        
class Child(Parent):
    
    def altered(self):
        print("CHILD, BEFORE PARENT altered()")
        super().altered()
        print("CHILD, AFTER PARENT altered()")
        
dad = Parent()
son = Child()

dad.altered()
print('=='* 20)
son.altered()

PARENT altered()
========================================
CHILD, BEFORE PARENT altered()
PARENT altered()
CHILD, AFTER PARENT altered()