Python @properties

Note below how x changed from a method to a property.


class A:
    def __init__(self):
        self._x = 0
	    
    def x(self):
        return self._x


A().x() # <-- This is a method

Above it’s defined as a method… now make it a property.


class A:
    def __init__(self):
        self._x = 0

    @property
    def x(self):
        return self._x


A().x # <-- Now properity 

Now the complete call with setter and deleter

Note the getter gets everytime when making an assignment.

class A:
    def __init__(self):
        self._x = 0

    @property
    def x(self):
        print("In getter!")
        print("x = {}".format(self._x))
        return self._x

    @x.setter
    def x(self, value):
        print("old value:{}  new value:{}".format(self.x, value))
    	self._x = value

    @x.deleter
    def x(self):
       	del self._x


a = A()
# We call the getter first
a.x = 3

"""
Here's the output:

  In getter
  x = 0
  old value:0  new value:3


"""


Python Exceptions


try:

    # raise ValueError('A very specific bad thing happened')
    raise Exception('A very specific bad thing happened', 'b')

except Exception as e:

    print(len(e.args))  # 2

    if e.args == ('A very specific bad thing happened', 'b'):
        print('Success')  # this will match

    if str(e) == "('A very specific bad thing happened', 'b')":
        print('yes this will print')

    print('e:{}'.format(str(e)))
    # e:('A very specific bad thing happened', 'b')



Python debugging

import pdb; pdb.set_trace()

Some commone commands: