Python Grammar: Things that I forget often

 

1. Use deep copy

list function copy() can be troublesome when the list has mutable objects.

from copy import deepcopy

l1 = [1, 2, [3, 4]]
l2 = l1.copy()
l3 = deepcopy(l1)
l1[1] = 3
l1[2][0] = 4
print(l2)
print(l3)

 

 

2. while--else for--else

else part is executed when the loop is stopped by 'break' or when the loop wasn't executed.

i = 0
while i > 10:
    print(i)
else:
    print('no')

for x in range(10):
    if x == 11:
        break
else:
    print('else part is activated if not broke')

 

3. Dictionary: get & pop

second parameter can be provided to each function

d = {'a': 'apple', 'b': 'banana', 'c': 'carrot'}
print(d.get('d', False))
print(d.pop('c', 'popped'))
print(d.pop('d', 'popped'))

 

4. Function parameter passing

def func(param1, param2, *args, **kwargs):
    print(f'param1: {param1}')
    print(f'param2: {param2}')

    print('args: ')
    for elem in args:
        print(elem)

    print('kwargs: ')
    for k, v in kwargs.items():
        print(k, v)


arr = [2, 3, '4']
dic = {'a': 'app', 'b': 'ban'}
func('p1', 'p2', *arr, **dic)

 

5. Wrapper

def document(func):
    def wrapper(*args, **kwargs):
        print(func.__name__)
        result = func(*args, **kwargs)
        print(result)
        return result
    return wrapper

@document
def iamfunc(a=1):
    return a + 3

x = iamfunc()
print(x)

 

6. Class properties

class Person:
    def __init__(self, name):
        self.__name = name

    @property
    def name(self):
        return self.__name

    @name.setter
    def name(self, name):
        self.__name = name

p = Person('Bob')
print(p.name)
p.name = 'Morgan'
print(p.name)

 

7. class method, static method

class A:
    count = 0
    def __init__(self):
        A.count += 1
    @classmethod
    def HowMany(cls):
        return A.count

a1 = A()
a2 = A()
a3 = A()
print(A.HowMany())

class A:
    @staticmethod
    def swapcase(str, type):
        if type == 'lower':
            return str.lower()
        elif type == 'upper':
            return str.upper()
        else:
            return None

print(A.swapcase('aBC', 'upper'))

 

8. Magic Method

class Complex:
    def __init__(self, real=0, imag=0):
        self.real = real
        self.imag = imag

    def __eq__(self, complex2):
        return self.real == complex2.real and self.imag == complex2.imag

    def __add__(self, complex2):
        return Complex(self.real+complex2.real, self.imag+complex2.imag)

    def __str__(self):
        return f"{self.real:3.3f}" + ' + ' + f"{self.imag:3.3f}" + "i"

c1 = Complex(3, 4)
c2 = Complex(3, 4)
print(c1 == c2)
print(c1 + c2)

 

9. Named Tuple

from collections import namedtuple

Point = namedtuple('Point', 'x y z')
p1 = Point(1, 2, 3)
print(p1.x, p1.y, p1.z)

p2 = Point('a', 'b', 'c')
print(p2.x, p2.y, p2.z)

 

10. Data Class

from dataclasses import dataclass

@dataclass
class Person:
    name: str
    hobby: str
    height: float
    age: int = 0

p1 = Person('Morgan', 'Game', 183.3, 28)
print(p1.name, p1.hobby, p1.height, p1.age)