Python Dictionary Insertion Order and Iteration

A command-line report prints settings in the order they were configured.

What You Need to Understand

Python dictionaries preserve the order in which keys were first inserted. Updating an existing key does not move it to the end, while deleting and re-adding can change its position.

When to Use It

A command-line report prints settings in the order they were configured.

Step-by-Step Python Example

settings = {"theme": "dark", "size": 12}
settings["theme"] = "light"
settings["autosave"] = True
for key in settings:
    print(key, settings[key])

How the Example Works

The existing theme stays first; autosave appears last. Iterating over a dictionary yields keys.

Example Output

theme light
size 12
autosave True
['b', 'a']

A Second Example

Compare this smaller variation with the main example, then experiment with your own values.

data = {"a": 1, "b": 2}
data.pop("a")
data["a"] = 3
print(list(data))

Important Behavior and Edge Cases

Dictionary order is not sorting; inserting keys in one order does not automatically alphabetize them.

Try It Yourself

Delete and reinsert the first key, then print the order again.

Common Beginner Mistakes

Dictionary order is not sorting; inserting keys in one order does not automatically alphabetize them.
Treating missing dictionary keys, replacement precedence, and shallow copies as if they had identical behavior in every context.

Key Takeaways

Python dictionaries preserve the order in which keys were first inserted.
The existing theme stays first; autosave appears last.
Dictionary order is not sorting; inserting keys in one order does not automatically alphabetize them.