Python 備忘單

• Python (python.org)
• 在 Y 分鐘內(nèi)學(xué)習(xí) X (learnxinyminute.com)
• python中的正則表達(dá)式 （quickref.me）

>>> print("Hello, World!")
Hello, World!

Python 中著名的“Hello World”程序

x = 4        # x is of type int
x = "Sally"  # x is now of type str
print(x)

Python 沒有用于聲明變量的命令。

mylist = []
mylist.append(1)
mylist.append(2)
for x in mylist:
    print(x) # prints out 1,2

a = 200
if a > 0:
    print("a is greater than 0")
else:
    print("a is not greater than 0")

for x in range(6):
    if x == 3: break
    print(x)
else:
    print("Finally finished!")

>>> def my_function():
...     print("Hello from a function")
...
>>> my_function()
Hello from a function

result = 10 + 30  # =>  40
result = 40 - 10  # =>  30
result = 50 * 5   # =>  250
result = 16 / 4   # =>  4
result = 25 % 2   # =>  1
result = 5 ** 3   # =>  125

counter = 0
counter += 10           # => 10
counter = 0
counter = counter + 10  # => 10

message = "Part 1."
# => Part 1.Part 2.
message += "Part 2."   

s = "Hello World"
s = 'Hello World'

a = """Multiline Strings
Lorem ipsum dolor sit amet,
consectetur adipiscing elit """

x = 1    # int
y = 2.8  # float
z = 1j   # complex

>>> print(type(x))
<class 'int'>

a = True 
b = False

bool(0)     # => False
bool(1)     # => True

list1 = ["apple", "banana", "cherry"]
list2 = [True, False, False]
list3 = [1, 5, 7, 9, 3]
list4 = list((1, 5, 7, 9, 3))

a = (1, 2, 3)
a = tuple((1, 2, 3))

類似于 List 但不可變

set1 = {"a", "b", "c"}   
set2 = set(("a", "b", "c"))

一組獨特的項目/對象

>>> empty_dict = {}
>>> a = {"one": 1, "two": 2, "three": 3}
>>> a["one"]
1
>>> a.keys()
dict_keys(['one', 'two', 'three'])
>>> a.values()
dict_values([1, 2, 3])
>>> a.update({"four": 4})
>>> a.keys()
dict_keys(['one', 'two', 'three', 'four'])
>>> a['four']
4

鍵 : 值(key : value)對，類JSON對象

整型

x = int(1)   # x will be 1
y = int(2.8) # y will be 2
z = int("3") # z will be 3

浮點型

x = float(1)     # x will be 1.0
y = float(2.8)   # y will be 2.8
z = float("3")   # z will be 3.0
w = float("4.2") # w will be 4.2

字符串

x = str("s1") # x will be 's1'
y = str(2)    # y will be '2'
z = str(3.0)  # z will be '3.0'

>>> a = "Hello, World"
>>> print(a[1])
e
>>> print(a[len(a)-1])
d

獲取索引為 1 處的字符（大多數(shù)的編程語言，默認(rèn)的索引都是從 0 開始。因此，索引為 1 ，代表列表中第 2 位的內(nèi)容）

>>> for x in "abc":
...     print(x)
a
b
c

循環(huán)遍歷單詞“abc”中的字母

>>> a = "Hello, World!"
>>> print(len(a))
13

len() 函數(shù)返回字符串的長度

>>> s = '===+'
>>> n = 8
>>> s * n
'===+===+===+===+===+===+===+===+'

>>> s = 'spam'
>>> s in 'I saw spamalot!'
True
>>> s not in 'I saw The Holy Grail!'
True

>>> s = 'spam'
>>> t = 'egg'
>>> s + t
'spamegg'
>>> 'spam' 'egg'
'spamegg'

>>> name = input("Enter your name: ")
Enter your name: Tom
>>> name
'Tom'

從控制臺獲取輸入數(shù)據(jù)

>>> "#".join(["John", "Peter", "Vicky"])
'John#Peter#Vicky'

>>> "Hello, world!".endswith("!")
True

>>> li1 = []
>>> li1
[]
>>> li2 = [4, 5, 6]
>>> li2
[4, 5, 6]
>>> li3 = list((1, 2, 3))
>>> li3
[1, 2, 3]
>>> li4 = list(range(1, 11))
>>> li4
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

>>> li = []
>>> li.append(1)
>>> li
[1]
>>> li.append(2)
>>> li
[1, 2]
>>> li.append(4)
>>> li
[1, 2, 4]
>>> li.append(3)
>>> li
[1, 2, 4, 3]

>>> li = ['bread', 'butter', 'milk']
>>> li.pop()
'milk'
>>> li
['bread', 'butter']
>>> del li[0]
>>> li
['butter']

>>> li = ['a', 'b', 'c', 'd']
>>> li[0]
'a'
>>> li[-1]
'd'
>>> li[4]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: list index out of range

>>> li = [3, 1, 3, 2, 5]
>>> li.count(3)
2

>>> li = ["re"] * 3
>>> li
['re', 're', 're']

a = 5
if a > 10:
    print("a is totally bigger than 10.")
elif a < 10:
    print("a is smaller than 10.")
else:
    print("a is indeed 10.")

>>> a = 330
>>> b = 200
>>> r = "a" if a > b else "b"
>>> print(r)
a

value = True
if not value:
    print("Value is False")
elif value is None:
    print("Value is None")
else:
    print("Value is True")

primes = [2, 3, 5, 7]
for prime in primes:
    print(prime)

animals = ["dog", "cat", "mouse"]
for i, value in enumerate(animals):
    print(i, value)

x = 0
while x < 4:
    print(x)
    x += 1  # Shorthand for x = x + 1

x = 0
for index in range(10):
    x = index * 10
    if index == 5:
    	break
    print(x)

for index in range(3, 8): 
    x = index * 10
    if index == 5:
    	continue
    print(x)

for i in range(4):
    print(i) # Prints: 0 1 2 3

for i in range(4, 8):
    print(i) # Prints: 4 5 6 7

for i in range(4, 10, 2):
    print(i) # Prints: 4 6 8

name = ['Pete', 'John', 'Elizabeth']
age = [6, 23, 44]
for n, a in zip(name, age):
    print('%s is %d years old' %(n, a))

def hello_world():  
    print('Hello, World!')

def add(x, y):
    print("x is %s, y is %s" %(x, y))
    return x + y

add(5, 6)    # => 11

def varargs(*args):
    return args

varargs(1, 2, 3)  # => (1, 2, 3)

def keyword_args(**kwargs):
    return kwargs

# => {"big": "foot", "loch": "ness"}
keyword_args(big="foot", loch="ness")

def swap(x, y):
    return y, x

x = 1
y = 2
x, y = swap(x, y)  # => x = 2, y = 1

def add(x, y=10):
    return x + y

add(5)      # => 15
add(5, 20)  # => 25

# => True
(lambda x: x > 2)(3)

# => 5
(lambda x, y: x ** 2 + y ** 2)(2, 1)

import math
print(math.sqrt(16))  # => 4.0

from math import ceil, floor
print(ceil(3.7))   # => 4.0
print(floor(3.7))  # => 3.0

from math import *

import math as m

# => True
math.sqrt(16) == m.sqrt(16)

import math
dir(math)

逐行

with open("myfile.txt") as file:
    for line in file:
        print(line)

帶行號

input = open('myfile.txt', 'r')
for i,line in enumerate(input, start=1):
    print("Number %s: %s" % (i, line))

寫一個字符串

contents = {"aa": 12, "bb": 21}
with open("myfile1.txt", "w+") as file:
    file.write(str(contents))

讀取字符串

with open('myfile1.txt', "r+") as file:
    contents = file.read()
print(contents)

寫一個對象

contents = {"aa": 12, "bb": 21}
with open("myfile2.txt", "w+") as file:
    file.write(json.dumps(contents))

讀取對象

with open('myfile2.txt', "r+") as file:
    contents = json.load(file)
print(contents)

import os
os.remove("myfile.txt")

import os
if os.path.exists("myfile.txt"):
    os.remove("myfile.txt")
else:
    print("The file does not exist")

import os
os.rmdir("myfolder")

class MyNewClass:
    '''This is a docstring.'''
    pass

# Class Instantiation
my = MyNewClass()

class Animal:
    def __init__(self, voice):
    self.voice = voice
 
cat = Animal('Meow')
print(cat.voice)    # => Meow
 
dog = Animal('Woof') 
print(dog.voice)    # => Woof

class Dog:

    # Method of the class
    def bark(self):
    print("Ham-Ham")
 
charlie = Dog()
charlie.bark()   # => "Ham-Ham"

class Employee:
    def __init__(self, name):
        self.name = name
 
    def __repr__(self):
        return self.name
 
john = Employee('John')
print(john)  # => John

class CustomError(Exception):
    pass

class ParentClass:
    def print_self(self):
        print('A')
 
class ChildClass(ParentClass):
    def print_self(self):
        print('B')
 
obj_A = ParentClass()
obj_B = ChildClass()
 
obj_A.print_self() # => A
obj_B.print_self() # => B

class ParentClass:
    def print_self(self):
        print("Parent")
 
class ChildClass(ParentClass):
    def print_self(self):
        print("Child")
 
child_instance = ChildClass()
child_instance.print_self() # => Child

class Animal: 
    def __init__(self, name, legs):
        self.name = name
        self.legs = legs
        
class Dog(Animal):
    def sound(self):
        print("Woof!")
 
Yoki = Dog("Yoki", 4)
print(Yoki.name) # => YOKI
print(Yoki.legs) # => 4
Yoki.sound()     # => Woof!

# This is a single line comments.

""" Multiline strings can be written
    using three "s, and are often used
    as documentation.
"""

''' Multiline strings can be written
    using three 's, and are often used
    as documentation.
'''

def double_numbers(iterable):
    for i in iterable:
        yield i + i

生成器可以幫助您編寫懶惰的代碼。

values = (-x for x in [1,2,3,4,5])
gen_to_list = list(values)

# => [-1, -2, -3, -4, -5]
print(gen_to_list)