python: sorting lists

Programming_Languages/Python/Syntax/Sorting_lists_in_Python.md

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+---
+categories:
+  - Programming Languages
+tags: [python]
+---
+
+# Sorting lists in Python
+
+### Using `sorted()` Function:
+
+The built-in `sorted()` function returns a new list containing all the elements of the original list sorted in the specified order (either ascending, which is default, or descending).
+
+```python
+my_list = [3, 1, 4, 1, 5, 9, 2, 6, 5]
+sorted_list = sorted(my_list)
+print(sorted_list)  # Output: [1, 1, 2, 3, 4, 5, 5, 6, 9]
+```
+
+For sorting in descending order, you can use the `reverse=True` argument:
+
+```python
+sorted_list_desc = sorted(my_list, reverse=True)
+print(sorted_list_desc)  # Output: [9, 6, 5, 5, 4, 3, 2, 1, 1]
+```
+
+### Using `.sort()` Method:
+
+The `.sort()` method sorts the elements of a list in-place and returns `None`. This modifies the original list.
+
+```python
+my_list = [3, 1, 4, 1, 5, 9, 2, 6, 5]
+my_list.sort()
+print(my_list)  # Output: [1, 1, 2, 3, 4, 5, 5, 6, 9]
+```
+
+For sorting in descending order:
+
+```python
+my_list.sort(reverse=True)
+print(my_list)  # Output: [9, 6, 5, 5, 4, 3, 2, 1, 1]
+```
+
+### Using a Custom Key Function:
+
+Both `sorted()` and `.sort()` accept a `key` parameter that allows you to specify a function to determine the sorting order. The function should take a single argument and return a value that will be used for sorting purposes.
+
+For example, if you have a list of strings and you want to sort them by their length:
+
+```python
+my_str_list = ["apple", "banana", "cherry", "date"]
+sorted_by_length = sorted(my_str_list, key=len)
+print(sorted_by_length)  # Output: ['date', 'apple', 'cherry', 'banana']
+```