The essentials
Quick reference
One focused task per row. Jump to the related section for complete, working examples.
| Use | Syntax | Examples |
|---|---|---|
| Create a list | items = ["alpha", "beta"] | View examples |
| Create from an iterable | items = list(range(1, 5)) | View examples |
| Read the first item | first = items[0] | View examples |
| Read the last item | last = items[-1] | View examples |
| Replace an item | items[1] = "updated" | View examples |
| Append one item | items.append("beta") | View examples |
| Append many items | items.extend(["gamma", "delta"]) | View examples |
| Remove by value | items.remove("beta") | View examples |
| Remove the last item | value = items.pop() | View examples |
| Remove by index | value = items.pop(0) | View examples |
| Slice a range | subset = items[1:4] | View examples |
| Slice with a step | subset = items[::2] | View examples |
| Reverse with slicing | reversed_items = items[::-1] | View examples |
| Transform every item | squares = [x ** 2 for x in items] | View examples |
| Filter items | evens = [x for x in items if x % 2 == 0] | View examples |
| Sort the existing list | items.sort() | View examples |
| Create a sorted copy | result = sorted(items) | View examples |
| Sort with a key | items.sort(key=str.lower) | View examples |
| Sort descending | items.sort(reverse=True) | View examples |
Python lists are ordered, mutable collections. They can hold mixed values, but code is usually clearer when each list contains one consistent kind of item.
Step by step
Detailed examples
Create lists with literals or constructors
List literals are clearest for known values. The list constructor is useful when consuming another iterable such as a range, tuple, or generator.
colors = ["blue", "green", "orange"]
numbers = list(range(1, 5))
print(colors)
print(numbers)['blue', 'green', 'orange']
[1, 2, 3, 4]Read and update items by index
Indexes begin at zero. Negative indexes count from the end, with -1 selecting the last item. An out-of-range index raises IndexError.
tasks = ["plan", "build", "test"]
print(tasks[0])
print(tasks[-1])
tasks[1] = "implement"
print(tasks)plan
test
['plan', 'implement', 'test']Append one item or extend with many
Append adds its argument as one item. Extend iterates over its argument and adds each value separately. Both mutate the existing list and return None.
languages = ["HTML", "CSS"]
languages.append("Python")
languages.extend(["SQL", "Bash"])
print(languages)['HTML', 'CSS', 'Python', 'SQL', 'Bash']Remove by value or position
Remove deletes the first matching value and raises ValueError when absent. Pop removes by index and returns the removed value; without an index, it uses the last item.
queue = ["Ada", "Linus", "Grace"]
queue.remove("Linus")
next_person = queue.pop(0)
print(next_person)
print(queue)Ada
['Grace']Select a range with slicing
The stop index is excluded. Any component may be omitted, and a negative step reverses direction. A simple full slice creates a shallow copy.
numbers = [0, 1, 2, 3, 4, 5]
print(numbers[1:4])
print(numbers[::2])
print(numbers[::-1])[1, 2, 3]
[0, 2, 4]
[5, 4, 3, 2, 1, 0]Transform and filter with comprehensions
A comprehension builds a new list. Keep it readable: when transformation or filtering needs several steps, use a normal loop or helper function instead.
numbers = range(1, 9)
even_squares = [number ** 2 for number in numbers if number % 2 == 0]
print(even_squares)[4, 16, 36, 64]Sort in place or return a sorted copy
List.sort changes the list and returns None. The sorted function accepts any iterable and returns a new list. Both support key and reverse arguments.
users = [
{"name": "Mina", "score": 82},
{"name": "Ravi", "score": 95},
{"name": "Jo", "score": 88},
]
ranking = sorted(users, key=lambda user: user["score"], reverse=True)
print([user["name"] for user in ranking])['Ravi', 'Jo', 'Mina']Local code tester
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Sources and further reading
References
Authoritative documentation used to verify and expand this cheat sheet.
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