• A quick cheatsheet on python operations

    • Slice:

      • astring = "Hello World"
print(astring[3:7]) # prints-> lo w
print(astring[0:10:2]) # skips one character, prints -> Hlowr
print(astring[::-1]) # reverse a string using step -1

    • Case

      • astring.upper()
astring.lower()

    • Slicing complete list performs a copy

      • spam_copy = spam[:]

    • Zip to loop

      • furniture = ['table', 'chair', 'rack', 'shelf']
price = [100, 50, 80, 40]

for item, amount in zip(furniture, price):
     print(f'The {item} costs ${amount}')

    • Multiple assignments

      • furniture = ['table', 'chair', 'rack', 'shelf']
table, chair, rack, shelf = furniture

      • find in list = furnitures.index('chaiur')

    • Sort:

      • reverse sort = furniture.sort(reverse=True)

      • sorted returns a new list, and accepts any iterable.

      • list.sort() sorts in place, only works for lists.

      • key function passed for custom sort

        >>> letters = ['a', 'z', 'A', 'Z']
>>> letters.sort(key=str.lower)
>>> letters
# ['a', 'A', 'z', 'Z']
>>> sorted(letters, key=str.lower) # also same

      • tuples are compared lexicographically; the first items are compared; if they are the same then the second items are compared, and so on.

    • Tuples:

      • tuples are immutable objects, lists are mutable.

      • Tuples are more memory efficient

    • Dictionary

      • >>> for key in pet.keys():
>>> for value in pet.values():
>>> for key, value in pet.items():

>>> pet.setdefault('has_hair', True)

# merge dictionaries
>>> dict_c = {**dict_a, **dict_b}

    • Set

      • >>> s = {1, 2, 3}
>>> s = set([1, 2, 3])

>>> s.add(4)
>>> s.update([2, 3, 4, 5, 6]) #add multiple
>>> s.remove(3) # raises errors
>>> s.discard(3) # does NOT raise errors

>>> s1.union(s2)  # or 's1 | s2'
>>> s1.intersection(s2, s3)  # or 's1 & s2 & s3'
>>> s1.difference(s2)  # or 's1 - s2'
>>> s1.symmetric_difference(s2)  # or 's1 ^ s2' all the elements that are not common between them.

    • Comprehension

      • # LIST COMPREHENSION

>>> new_list = [n for n in names]
>>> n = [(a, b) for a in range(1, 3) for b in range(1, 3)]
# [(1, 1), (1, 2), (2, 1), (2, 2)]
>>> new_list = [n for n in names if n.startswith('C')]

# SET COMPREHENSION
>>> {s.upper() for s in b}

# DICT COMPREHENSION
>>> {v: k for k, v in c.items()}

    • Strings

      • >>> ', '.join(['cats', 'rats', 'bats'])

  • References