Python lists with trailing comma

In Python, you might have stumbled across lists ending with a trailing comma. Surprisingly, Python allows it, considering it as a valid syntax:

python> ["banana", "apple", "pear",]
["banana", "apple", "pear"]

There are multiple advantages adopting this convention. Ending your Python list with a trailing comma makes the list easier to edit – reducing the clutter in the git diff outcome – and makes future changes (e.g. adding an item to the list) less error-prone.

Reducing git diff clutter

Especially when your list is multi-lines, having a trailing comma makes the list easier to edit, reducing the clutter in the git diff outcome your version control framework presents to you.

Changing the following list:

names = [
    "Charles de Gaulle",
    "Antoine de Saint-Exupéry",
]

to:

names = [
    "Charles de Gaulle",
    "Antoine de Saint-Exupéry",
    "Bernard Clavel",
]

only involves a one-line change:

names = [
    "Charles de Gaulle",
    "Antoine de Saint-Exupéry",
+   "Bernard Clavel",
]

versus a confusing 3 multi-lines difference git output otherwise:

names = [
    "Charles de Gaulle",
-   "Antoine de Saint-Exupéry"
+   "Antoine de Saint-Exupéry",
+   "Bernard Clavel"
]

No more breaking changes

Another advantage of having trailing commas in your Python lists is that it makes changes less error-prone (with the risk of missing a comma when adding a new item into the list):

names = [
    "Charles de Gaulle",
    "Antoine de Saint-Exupéry"
    "Bernard Clavel"
]

Note: the above list is syntactically valid but will not return the expected outcome. Instead, it will trigger an implicit string literal concatenation.

['Charles de Gaulle', 'Antoine de Saint-ExupéryBernard Clavel']