python 基础语法笔记

l = [1, 2, 3, 4]

tup = (1, 2, 3, 4)

list((1, 2, 3))
[1, 2, 3]
l.count(3)
l.index(7)
l.reverse()
l.sort()
l.append(4)
# extend会将里面的元素添加进去，而append会直接将[1,2]作为一个元素加入
l.extend([1,2])

tuple([1, 2, 3])
(1, 2, 3)
tup.count(3)
tup.index(7)
list(reversed(tup))
sorted(tup)

# 初始化
d1 = {'name': 'jason', 'age': 20, 'gender': 'male'}
d2 = dict({'name': 'jason', 'age': 20, 'gender': 'male'})
d3 = dict([('name', 'jason'), ('age', 20), ('gender', 'male')])
d4 = dict(name='jason', age=20, gender='male') 
d1 == d2 == d3 == d4
True

# 赋值
d['name']= 'xiaoming'

# 获取值
d['name']
d.get('name')
d.get('name', 'null')

# 删除
d.pop('name')

# 是否存在
'name' in d
True

# 排序
d = {'b': 1, 'a': 2, 'c': 10}
d_sorted_by_key = sorted(d.items(), key=lambda x: x[0]) # 根据字典键的升序排序
d_sorted_by_value = sorted(d.items(), key=lambda x: x[1]) # 根据字典值的升序排序d_sorted_by_key

# 初始化
s1 = {1, 2, 3}
s2 = set([1, 2, 3])
s1 == s2
True

# 基操
s.add(4)
s.remove(1)
sorted(s)

# 一样的
'123'
"123"
"""123"""

name = 'jack'
name[0]
name[1:3]

# 遍历
for char in name
	print(char)

# 替换
s.replace('h', 'n')

# 连接
s += 'a'
'-'.join(['aaa','bbb'])

# 分离
'1-1-1-1-2'.split('-')

# 去掉开头结尾
string.strip(str)
string.ltrip(str)
string.rtrip(str)

# 从开始到结尾进行查找
string.find(sub, start, end)

# 数字到字符串，字符串到数字
str(1)
int('1')

# 格式化
>>> print('id: {}, name: {}'.format("1", "xiaowang"))
id: 1, name: xiaowang

name = input('your name:')

with open('in.txt', 'r') as fin:
    text = fin.read()

with open('out.txt', 'w') as fout:
    fout.write('123')

# 序列化对象为json字符串
json.dumps(params)

# 反序列化json字符串
json.loads(params_str)

if id == 0:
    print('red')
elif id == 1:
    print('yellow')
else:
    print('green')

l = [1, 2, 3, 4]

# 遍历元素
for item in l:
    print(item)

# 遍历下标
for index in range(0, len(l)):
    if index < 5:
        print(l[index])

# 下标和元素同时需要，使用enumerate
for index, item in enumerate(l):
    if index < 5:
        print(item)

# while当然也可以
while index < len(l):
    print(l[index])
    index += 1

# 单行操作，很简洁
expression1 if condition else expression2 for item in iterable

for item in iterable:
    if condition:
        expression1
    else:
        expression2

expression1 for item in iterable if condition

for item in iterable:
    if condition:
        expression1

try:
    s = input('please enter two numbers separated by comma: ')
    num1 = int(s.split(',')[0].strip())
    num2 = int(s.split(',')[1].strip())
    ... 
except ValueError as err:
    print('Value Error: {}'.format(err))
finally:
    print('finally')

print('continue')
...

except (ValueError, IndexError) as err:

# OR
except ValueError as err:
    print('Value Error: {}'.format(err))
except IndexError as err:
    print('Index Error: {}'.format(err))
except:
    print('Other error')

# 自定义异常
class MyInputError(Exception):
    """Exception raised when there're errors in input"""
    def __init__(self, value): # 自定义异常类型的初始化
        self.value = value
    def __str__(self): # 自定义异常类型的 string 表达形式
        return ("{} is invalid input".format(repr(self.value)))
    
try:
    raise MyInputError(1) # 抛出 MyInputError 这个异常
except MyInputError as err:
    print('error: {}'.format(err))

# 不需要申明类型
def my_sum(a, b):
    return a + b

# 设置默认值
def func(param = 0):

# 函数定义嵌套，内部函数无法被外部直接调用
def f1():
    print('hello')
    def f2():
        print('world')
    f2()
f1()

def outer():
    x = "local"
    def inner():
        nonlocal x # nonlocal 关键字表示这里的 x 就是外部函数 outer 定义的变量 x
        x = 'nonlocal'
        print("inner:", x)
    inner()
    print("outer:", x)
outer()
# 输出
inner: nonlocal
outer: nonlocal

# 闭包，就是返回一个函数而已
def nth_power(exponent):
    def exponent_of(base):
        return base ** exponent
    return exponent_of # 返回值是 exponent_of 函数
 
square = nth_power(2) # 计算一个数的平方
cube = nth_power(3) # 计算一个数的立方

lambda argument1, argument2,... argumentN : expression

square = lambda x: x**2
square(3)

# map函数，对于集合内每个元素都做一次func
l = [1, 2, 3, 4, 5]
new_list = map(lambda x: x * 2, l) # [2， 4， 6， 8， 10]

# filter函数，对于集合内每个元素都做一次func，并返回true或者false，结果返回为true的集合
l = [1, 2, 3, 4, 5]
new_list = filter(lambda x: x % 2 == 0, l) # [2, 4]

# reduce函数，集合内每个元素都做一次func，最后将结果组合
l = [1, 2, 3, 4, 5]
product = reduce(lambda x, y: x * y, l) # 1*2*3*4*5 = 120

class Document():
    
    WELCOME_STR = 'Welcome! The context for this book is {}.'
    
    def __init__(self, title, author, context):
        print('init function called')
        self.title = title
        self.author = author
        self.__context = context
    
    # 类函数
    @classmethod
    def create_empty_book(cls, title, author):
        return cls(title=title, author=author, context='nothing')
    
    # 成员函数
    def get_context_length(self):
        return len(self.__context)
    
    # 静态函数
    @staticmethod
    def get_welcome(context):
        return Document.WELCOME_STR.format(context)
 
 
empty_book = Document.create_empty_book('What Every Man Thinks About Apart from Sex', 'Professor Sheridan Simove')
 
 
print(empty_book.get_context_length())
print(empty_book.get_welcome('indeed nothing'))
 
########## 输出 ##########
 
init function called
7
Welcome! The context for this book is indeed nothing.

# 引入utils包下的util文件的get_sum方法
from utils.utils import get_sum

# 直接从项目根目录中导入，并依次向下导入模块 mat.py 中的 Matrix
from proto.mat import Matrix

import module_name
from module_name import *