When we do python programing, I find there are many tricks and skills to make our code more pythonic and more effectively.
Here I collect them, and keep this post continuously updated.
String Operation
F string formatting
The Official name of this kind of grammar is Literal String Interpolation, a new characteristic in python3.6. Here are some examples.
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name = "Eric"
age = 74
f"Hello, {name}. You are {age}."
# output:
# Helle, Eric. You are 74.
F"Hello, {name}. You are {age}."
# capital F is okay.
You can put any expression in the { }. Even you can write a sentence in several lines.
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# type 1
message = (f"Hi {name}. "
f"You are a {profession}. "
f"You were in {affiliation}.")
# output: 'Hi Eric. You are a comedian. You were in Monty Python.'
# type 2
message = (f"Hi {name}. "
"You are a {profession}. "
"You were in {affiliation}.")
# output: 'Hi Eric. You are a comedian. You were in Monty Python.'
# type 3
message = f"""
Hi {name}.
You are a {profession}.
You were in {affiliation}.
"""
# output: '\n Hi Eric. \n You are a comedian. \n You were in Monty Python.\n '
如果!, :或}不在括号，大括号，括号或字符串中，则它将被解释为表达式的结尾。 可以通过将这些符号嵌套在圆括号中来解决此问题。
How to distinguish number / alphabet in string
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str_1 = "123"
str_2 = "Abc"
str_3 = "123Abc"
#用isdigit函数判断是否数字
print(str_1.isdigit())
Ture
print(str_2.isdigit())
False
print(str_3.isdigit())
False
#用isalpha判断是否字母
print(str_1.isalpha())
False
print(str_2.isalpha())
Ture
print(str_3.isalpha())
False
#isalnum判断是否数字和字母的组合
print(str_1.isalnum())
Ture
print(str_2.isalnum())
Ture
print(str_1.isalnum())
Ture
Tips: If string contains other characters, like space, False will also be returned.
Advanced Functions
-
lambda
Anonymous fuction
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lambda x,y:x+y lambda argument_list: expresstion ''' argument list is like common python functions, like "a, b / a=1, b=2 / *args / **kwargs /a, b=1, *args" are all okay expression means the return, it's needed to mention that expression must be in one line '''
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map(function, sequence)
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def f(x): return x**2 map(f, range(10)) ''' f: ONE-variable function map() means apply function f to each element of the sequence, and return a new sequence '''
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reduce(function, sequence)
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def f(x, y): return x+y reduce(f, range(10)) ''' f: TWO-variable function reduce() means that apply f to result of first two elements from f and the next element iteractively reduce(f, [x1,x2,x3,x4]) = f(f(f(x1,x2),x3),x4) '''
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filter(function, sequence)
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def is_odd(s): return n%2==1 filter(is_odd, range(10)) # output: [1,3,5,7,9] ''' f: filter function, return True or False filter() means that we apply f to each element of sequence and have judgements respectively, if false, drop that element and keep the true, return filtered sequence finally. '''
Decorator
Example first:
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def dec1(func): # decorator
print("1111")
def one(): # wrapper
print("2222")
func()
print("3333")
return one
def dec2(func):
print("aaaa")
def two():
print("bbbb")
func()
print("cccc")
return two
@dec1
@dec2
def test():
print("test test")
if __name__ == '__main__':
test()
Output:
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aaaa
1111
2222
bbbb
test test
cccc
3333
Meanwhile:
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@dec1
def test1():
print('test')
def test2():
print('test')
test2 = dec1(test2)
test1()
test2()
# test1() and test2() have the same output
多个decorator的执行顺序是从最后一个开始，直到第一个装饰器，再顺序执行wrapper，以及被装饰的function。
引入decorator装饰器的目的是为了__动态的给函数加上功能__，通过代码复用完成对函数的修改，减少对函数本身代码的反复修改。
Common Decorator
@property：将一个类的方法变成类属性去调用
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class Student(object):
@property
def score(self):
return self._score
@score.setter
def score(self, value):
if not isinstance(value, int):
raise ValueError('score must be an integer!')
if value < 0 or value > 100:
raise ValueError('score must between 0 ~ 100!')
self._score = value
@property
def gpa(self):
if score > 85:
return 4
elif score > 75:
return 3
elif score > 65:
return 2
else:
return 0
把一个getter方法变成属性，只需要加上@property就可以了，此时，@property本身又创建了另一个装饰器@score.setter，负责把一个setter方法变成属性赋值，于是，我们就拥有一个可控的属性操作。只定义getter方法，不定义setter方法就是一个只读属性 。
