Tips And Tricks
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
[]