Working with Python

Control Flow

Conditionals

Basic if conditionals

The basic if syntax in Python, with elif (else if) and else:

x = 5
if x > 0:
    print(f"{x} is positive")
elif x < 0:
    print(f"{x} is negative")
else:
    print("Zero. Your number is zero.")

Ternary operator

Python doesn't have a specific ternary operator instead you can use if-else inline in the form a if condition else b Note: the else portion is required.

x = 5
is_negative: False if x >= 0 else True

Match statement

The match statement was introduced in Python 3.10 and can match patterns given in one or more case blocks.

match num:
    case 1:
        print("One - Not prime by definition")
    case 2 | 3 | 5 | 7:
        print("Prime number")
    case 4 | 6 | 8 | 9:
        print("Not prime")
    case _:
        print("Shrug")

The case _ is a catch all and will match anything not yet matched.

Multiple values can be included in a case separated by the | for or.

The objects being compared and matched don't have to be simple values.

# Rock-paper-scissor tuple
match throw:
    case ("r", "r") | ("p", "p") | ("s", "s"):
        print("Tie")
    case ("r", "s") | ("p", "r") | ("s", "p"):
        print("Win")
    case ("r", "p") | ("p", "s") | ("s", "r"):
        print("Lose")
    case _:
        print("Bad throw")

Loops

Use the range() function to create a for loop iterator:

for x in range(3):
    print(x)
>>> 0
>>> 1
>>> 2

Pass two parameters to range() to specify a start, stop:

for x in range(5, 8):
    print(x)
>>> 5
>>> 6
>>> 7

Pass three parameters to range() to specify a start, stop, and step:

for x in range(1, 10, 3):
    print(x)
>>> 1
>>> 4
>>> 7

If you want to count backward using range() using a negative step:

for x in range(5, -1, -1):
    print(x)
>>> 5
>>> 4
>>> 3
>>> 2
>>> 1
>>> 0

Iterators

Many Python objects are iterable, these include strings, lists, dicts, and sets.

s = "abc"
for ch in s:
    print(ch)
>>> a
>>> b
>>> c

Iterating over lists in Python:

v = ["a", "b", "c"]
for el in v:
    print(el)
>>> a
>>> b
>>> c

Use .items() method to iterate over dicts in Python with key, value pair:

d = { 'a': 'apple', 'b': 'banana', 'c': 'cherry' }
for k,v in d.items():
    print(k, v)
>>> a apple
>>> b banana
>>> c cherry

Enumerate

Use the enumerate() function to iterate with an index:

a = ["a", "b", "c"]
for idx, item in enumerate(a):
    print(f"{idx} -> {item}")
0 -> a
1 -> b
2 -> c
>>>