Find Out what Attributes an Object has

dir(object)

Find out the Type of Obejct

type(object)

Clear the python terminal screen

ctrl + l

Merge 2 dicts

Must be Python3.5+ and will give preference to 2nd dict

    >>> x = {'a': 1, 'b': 2}
    >>> y = {'b': 3, 'c': 4}
    >>> z = {**x, **y}
    >>> z
    {'a': 1, 'b': 3, 'c': 4}

Testing Multiple flags

    x, y, z = 0, 1, 0

    if x == 1 or y == 1 or z == 1:
        print('passed')

    if 1 in (x, y, z):
        print('passed')

    if x or y or z:
        print('passed')

    if any((x, y, z)):
        print('passed')

A dicts get() method has a default argument

    >>> names = {1: "surfer", 2: "joe sloan", 3: "tam lovelace"}
    >>> f'Hi, {names.get(1)}'
    'Hi, surfer'
    >>> f'Hi, {names.get(4, "there!")}'
    'Hi, there!'

Named tuples instead of a class

    >>> Car = namedtuple('Car', 'colour mileage')
    >>> my_gti = Car('red', 126713.2)
    >>> my_gti
    Car(colour='red', mileage=126713.2)
    >>> type(my_gti)
    <class '__main__.Car'>
    >>> my_gti.colour
    'red'

Remember namedtuple is immutable, like a normal tuple

    >>> my_gti.colour = 'blue'
    Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
    AttributeError: can't set attribute

Prett print JSON

    >>> gti = {'rims': 18, 'top_speed':235, 'power':147}
    >>> import json
    >>> print(json.dumps(gti, indent=4, sort_keys=True))
    {
        "power": 147,
        "rims": 18,
        "top_speed": 235
    }

Function argument unpacking

    def myfunc(x, y, z):
        print(x, y, z)

    tuple_vec = (1, 0, 1)
    dict_vec = {'x': 1, 'y': 0, 'z': 1}

Remember * means treat this as an iterable

    >>> myfunc(*tuple_vec)
    1, 0, 1

Remember ** means treat this as a dict

    >>> myfunc(**dict_vec)
    1, 0, 1

In-place variable swapping

No need for a temporary variable

    >>> a = 45
    >>> b = 10
    >>> a, b = b, a
    >>> b
    45
    >>> a
    10

Is vs “==”

  • “is” expressions evaluate to True if two
  • ”==” evaluates to True if the objects

      >>> opp = [1, 2, 3]
      >>> rod = [1, 2, 3]
      >>> opp == rod
      True
      >>> opp is rod
      False
      >>> rod = opp
      >>> opp is rod
      True
    

Function are first-class citizens

They can be passed as arguments, returned as values and assigned to variables and stored in data structures

    >>> def myfunc(a, b):
    ...     return a + b
    ...
    >>> funcs = [myfunc]
    >>> funcs[0]
    <function myfunc at 0x107012230>
    >>> funcs[0](2, 3)
    5

Dicts can be used as a switch statement

A lambda is just an unnamed function

    def dispatch_dict(operator, x, y):
        return {
            'add': lambda: x + y,
            'sub': lambda: x - y,
            'mul': lambda: x * y,
            'div': lambda: x / y,
        }.get(operator, lambda: None)()

List comprehension

    vals = [expression 
            for value in collection 
            if condition]

Equivalent to:

    vals = []
    for value in collection:
        if condition:
            vals.append(expression)

Example:

    >>> vals = list(range(1, 11))
    >>> vals
    [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
    >>> evens = [x for x in vals if x % 2 == 0]
    >>> evens
    [2, 4, 6, 8, 10]

Delete all items from alist

    >>> lst = list(range(0, 6))
    >>> lst
    [0, 1, 2, 3, 4, 5]
    >>> del lst[:]
    >>> lst
    []

Source

Dan Bader Python Tips