5 // -3 # => -2
-5.0 // 3 # => -2.0
5.2 % 3 # => 2.2
5 ** 3 # => 125
True * 8 # => 8
False - 5 # => -5
bool({}) # => False
'cool' if 3 > 2 else 'bad'-
除法
/结果自动转换为小数，整除//为地板除 -
布尔值
True==1 False==0与布尔运算not and or -
bool()只有 3 个结果为False：None 0 空strings/lists/dicts/tuples -
is是看两个变量是不是指向同一个对象，==是看两个对象是不是有相同的值 -
没有三目运算符
?:，等价的有true_ans if condition else wrong_ans
'hello ' + "world" + '!' # => 'hello world!'
'hello world!'[6] # => 'w'
'{} can be {}'.format('string', 'interpolated')
'{0} be nimble, {0} be quick, {1} be large'.format('Jack', 'Tim')
'{name} is {age}'.format(name='Bob', age=20)
'%s xxx %s' % ('str', 'str')
'%s can be %s the %s way' % ('Strings', 'interpolated', 'old')-
'{}'.format(str)格式化字符串输出 -
之前的方式为
'%s' % (str)
# 构造队列
# 方法有：append(x) appendleft(x)
# pop() popleft()
from collections import deque
q = deque(maxlen=5)
q.append(2)
q.appendleft(1)
q.pop()
q.popleft()# 统计词频
# 还可以执行 + - 运算
from collections import Counter
words = [
'look', 'into', 'my', 'eyes', 'look', 'into', 'my', 'eyes',
'the', 'eyes', 'the', 'eyes', 'the', 'eyes', 'not', 'around', 'the',
'eyes', "don't", 'look', 'around', 'the', 'eyes', 'look', 'into',
'my', 'eyes', "you're", 'under'
]
morewords = ['why','are','you','not','looking','in','my','eyes']
word_counts =Counter(words)
print(word_counts)
zipped = word_counts.most_common()
words_c, count_w = zip(*zipped)
print(words_c)
print(count_w)
word_counts.update(morewords)
print(word_counts)
a = Counter(words)
b = Counter(morewords)
print(a,b,a+b,a-b,sep='\n')# mutable
li.insert(i, x): 在 index i 处添加 x，只能添加一个
li.pop(i) : 在 i 处删除元素，只能删除一个
li.remove(x) : 删除第一个值为 x 的元素
del li[start:stop:step]: 随意删
clear() / copy() / reverse() / sort()
append(x) / extend(list) / lista + listb
count(x) / index(x)
li *= n
len(li) / x in li# tuple 元素不能修改，自带的括号可以省略。可以使用 + 和 del。常用做交换。
a, *b, c = (1, 2, 3, 4) # => b == [3, 4]
a, b = b, a # => tuple 快速交换# set 集合有交(&) 并(|) 补(-)
# add 方法添加新项
# a <= b 可以检查 a 是 b 的子集吗
one_set = set({1, 2, 3, 4, 5})
other_set = {4, 5, 6, 7}
print(one_set & other_set) # => {4, 5}
print(one_set | other_set) # => {1, 2, 3, 4, 5, 6, 7}
print(one_set - other_set) # => {1, 2, 3}dict.keys() / dict.values() / dict.items()
dict.update(newdict)
dict.get(keyname)
dict.setdefault(keyname, value)-
元组（tuple）：小括号（可省略）、可以有相同元素、不可改只能读
-
列表(list)：中括号、可以有相同元素、可以进行增删改查
-
集合(set)：大括号、不存放相同元素，创建用 set()
import os
import json
datas = []
open with(fp) as f:
for l in f:
line = json.loads(l)
datas.append(line)
open with(fn, 'w') as f:
f.write(os.linesep.join([
json.dumps(i, ensure_ascii=False) for i in datas
]))some_var = 5
if some_var > 10:
print("some_var比10大")
elif some_var < 10: # elif句是可选的
print("some_var比10小")
else: # else也是可选的
print("some_var就是10")for animal in ["dog", "cat", "mouse"]:
print("{} is a mammal".format(animal))x = 0
while x < 4:
print(x)
x += 1 # x = x + 1 的简写# 用try/except块处理异常状况
try:
# 用raise抛出异常
raise IndexError("This is an index error")
except IndexError as e:
pass # pass是无操作，但是应该在这里处理错误
except (TypeError, NameError):
pass # 可以同时处理不同类的错误
else: # else语句是可选的，必须在所有的except之后
print("All good!") # 只有当try运行完没有错误的时候这句才会运行def connect_to_next_port(self, minimum):
'''Connects to the next available port.
Args:
minimum: A port value greater or equal to 1024.
Raises:
ValueError: if the minimum port specified is less than 1024.
ConnectionError: If no available port is found.
Returns:
The new minimum port.
'''
if minimum < 1024:
raise VlueError('Minimum port must be at least 1024, not %d.' % (minimum,))
port = self._find_next_open_port(minimum)
if not port:
raise ConnectionError('Could not connect to service on %d or higher.' % (minimum,))
assert port >= minimum, 'Unexpected port %d when minimum was %d.' % (port, minimum)
return port# iter(x) 构造迭代器，next(i) 不停的往后取值
somedict = {1:a, 2:b, 3:c}
i = iter(somedict.keys())
next(i) # 1
i.__next__() # 2def all_the_args(*args, **kwargs):
print(args) # (1, 'a', 1, 2, 3, 4)
print(kwargs) # {'a': 3, 'b': 4}
args = (1, 2, 3, 4)
kwargs = {"a": 3, "b": 4}
all_the_args(1, 'a', *args, **kwargs)x = 5
def setX(num):
# 局部作用域的x和全局域的x是不同的
x = num # => 43
print ('local:', x) # => 43
def setGlobalX(num):
global x
print ('global:',x) # => 5
x = num # 现在全局域的x被赋值
print ('global:',x) # => 6
setX(43)
setGlobalX(6)
print('global:', x) # 6# lambda 匿名函数
(lambda x: x > 2)(3)seasons = ['a', 'b', 'c', 'd']
list(enumerate(seasons)) # [(0, 'a'), (1, 'b'), (2, 'c'), (3, 'd')]x = [1, 2, 3]
y = [4, 5, 6]
z = [7, 8, 9]
list(zip(x, y, z)) ## [(1, 4, 7), (2, 5, 8), (3, 6, 9)]class Human:
# class attribute
species = "H.sapiens"
# basic inititalizer, this is callled when this class is instantiated.
def __init__(self, name):
self.name = name
self.age = 0
# instance method
def say(self, msg):
print("{name}: {message}".format(name=self.name, message=msg))
def sing(self):
return 'yo... yo... yo...'
#class method is shared among all instances
@classmethod
def get_species(cls):
return cls.species
# static method is called without a class or instance reference
@staticmethod
def grunt():
return "*grunt*"
# a property is just like a getter
@property
def age(self):
return self._age
# corresponding setter
@age.setter
def age(self, age):
self._age = age
# corresponding deleter
@age.deleter
def age(self):
del self._age
# 示例
print('instantiate a class:')
i = Human(name="Ian")
i.say("hi") # "Ian: hi"
j = Human(name="Joel")
j.say("hello") # "Joel: hello"
print('\ncall class method:')
i.say(i.get_species()) # Ian: H.sapiens
Human.species = 'H.neanderthalensis'
i.say(i.get_species()) # Ian: H.neanderthalensis
j.say(j.get_species()) # Joel: H.neanderthalensis
print('\ncall static method:')
print(Human.grunt()) # => "*grunt*"
print('\nupdate property, use setter getter deleter:')
i.age = 42
i.say(i.age) # => "Ian: 42"
j.say(j.age) # => "Joel: 0"
del i.age
j.say(j.age) # => "Joel: 0"
i.say(i.age) # => raise an AttributeError: 'Human' object has no attribute '_age'# Inheritance
class Superhero(Human):
# override parents' attributes
species = 'Superhuman'
# constructor
def __init__(self, name, movie=False, superpowers=['super strengh', 'bulletproofing']):
self.fictional = True
self.movie = movie
self.superpowers = superpowers
# call parent class constructor
super().__init__(name)
# override sing method
def sing(self):
return 'Dun, dun, DUN!'
def boast(self):
for power in self.superpowers:
print('I wield the power of {power}'.format(power=power))
# 示例
sup = Superhero(name='Tick')
if isinstance(sup, Human):
print('I am human')
if type(sup) is Superhero:
print('I am a superhero')
# Get the Method Resolution search Order
print(Superhero.__mro__) # (<class '__main__.Superhero'>, <class '__main__.Human'>, <class 'object'>)
print('Am I Oscar eligible? ' + str(sup.movie)) # Am I Oscar eligible? False# another class definition for multiple inheritance
class Bat:
species = 'Baty'
def __init__(self, can_fly=True):
self.fly = can_fly
def say(self, msg):
msg = '... ... ...'
return msg
def sonar(self):
return '))) ... ((('
b = Bat()
print(b.say('hello')) # ... ... ...
print(b.fly) # True
# multiple inheritance
class Batman(Superhero, Bat):
def __init__(self, *args, **kwargs):
# 一般是这样继承: super(Batman, self).__init__(*args, **kwargs)
Superhero.__init__(self, 'anonymous', movie=True, superpowers=['Wealthy'], *args, **kwargs)
Bat.__init__(self, *args, can_fly=False, **kwargs)
self.name = 'Sad Affleck'
def sing(self):
return 'nan nan nan nan nan batman!'
supman = Batman()
print(Batman.__mro__) # (<class '__main__.Batman'>, <class '__main__.Superhero'>, <class '__main__.Human'>, <class '__main__.Bat'>, <class 'object'>)
print('\n' + supman.get_species()) # Superhuman
print(supman.sing()) # nan nan nan nan nan batman!
print(supman.sonar()) # ))) ... (((
supman.age = 100
print(supman.age) # 100
print('Can I fly?\nans: ' + str(supman.fly)) # False
print(supman.__dict__)
{'fictional': True,
'movie': True,
'superpowers': ['Wealthy'],
'name': 'Sad Affleck',
'_age': 100,
'fly': False}# Decorator
from functools import wraps
from time import time
def timer(func):
@wraps(func)
def wrapper(*args, **kwargs):
before = time()
rv = func(*args, **kwargs)
print('%s(%r,%r) -> %r'%(func.__name__, args, kwargs, rv))
after = time()
print('time token:', after - before)
return rv
return wrapper
@timer
def sum(a, b=10):
return a+b
sum(2)
# sum((2,),{}) -> 12
# time token: 0.00024509429931640625result = [mapping_expr for value in iterable if filter_expr]
result = [{'key': value} for value in iterable
if a_long_filter_expression(value)]
result = [complicated_transform(x)
for x in iterable if predicate(x)]
descriptive_name = [
transform({'key': key, 'value': value}, color='black')
for key, value in generate_iterable(some_input)
if complicated_condition_is_met(key, value)
]
result = []
for x in range(10):
for y in range(5):
if x * y > 10:
result.append((x, y))
return {x: complicated_transform(x)
for x in long_generator_function(parameter)
in x is not None}
squares_generator = (x**2 for x in range(10))
unique_names = {user.name for user in users if user is not None}
eat(jelly_bean for jelly_bean in jelly_beans
if jelly_bean.color == 'black')import matplotlib.pyplot as plt
hist = {
'epoch': [1, 2, 3, 4, 5],
'mae': [1, 2, 3, 4, 5],
'val_mae': [1, 2.1, 3.2, 4.3, 5.4],
'mse': [1, 2, 3, 4, 5],
'val_mse': [1, 2.1, 3.2, 4.3, 5.4],
}
def plot_history(hist):
plt.figure(figsize=(16,10))
plt.xlabel('Epoch')
plt.ylabel('Mean Abs Error [MPG]')
plt.plot(hist['epoch'], hist['mae'], label='Train Error')
plt.plot(hist['epoch'], hist['val_mae'], label='Val Error')
plt.ylim([0, 5])
plt.legend()
plt.figure()
plt.xlabel('Epoch')
plt.ylabel('Mean Square Error [$MPG^2$]')
plt.plot(hist['epoch'], hist['mse'], label='Train Error')
plt.plot(hist['epoch'], hist['val_mse'], label='Val Error')
plt.ylim([0, 20])
plt.legend()
plt.show()
plot_history(hist)