Hey everyone,<\/p>\n\n\n\n
I\u2019m currently learning Python and working with dictionaries. I know how to create one, but now I need to iterate through a dictionary in Python to access both the keys and the values.<\/p>\n\n\n\n
What\u2019s the proper way to do this? Should I loop over the keys, values, or both? And what if I want to update values as I go? Would appreciate examples and best practices!<\/p>\n\n\n\n
Thanks in advance.<\/p>\n\n\n\n
Great question and one every Python developer asks at some point! Whether you’re processing image metadata, user preferences, or API responses, you\u2019ll often need to iterate through a dictionary in Python.<\/p>\n\n\n\n
Let\u2019s break down all the different ways you can do it and when to use each.<\/p>\n\n\n\n
A dictionary in Python is a collection of key-value pairs, like so:<\/p>\n\n\n
image = {\n\n\u00a0\u00a0\u00a0\u00a0\"filename\"<\/span>: \"sunset.jpg\"<\/span>,\n\n\u00a0\u00a0\u00a0\u00a0\"width\"<\/span>: 1920<\/span>,\n\n\u00a0\u00a0\u00a0\u00a0\"height\"<\/span>: 1080<\/span>,\n\n\u00a0\u00a0\u00a0\u00a0\"format\"<\/span>: \"JPEG\"<\/span>\n\n}<\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\nYou can access values with image[\"width\"]<\/code>, but when you want to process all the entries, like exporting or modifying data, you\u2019ll need to iterate.<\/p>\n\n\n\n1. Iterate Over Keys<\/h2>\n\n\n\n
This is the most basic loop:<\/p>\n\n\n
for<\/span> key in image:\n\n\u00a0\u00a0\u00a0\u00a0print<\/span>(key)<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\nOr:<\/p>\n\n\n
for<\/span> key<\/span> in<\/span> image<\/span>.keys<\/span>():\n\n\u00a0\u00a0\u00a0\u00a0print<\/span>(key<\/span>)<\/code><\/span>Code language:<\/span> CSS<\/span> (<\/span>css<\/span>)<\/span><\/small><\/pre>\n\n\nUse this when you only need the keys and don\u2019t care about the values.<\/p>\n\n\n\n
2. Iterate Over Values<\/h2>\n\n\nfor<\/span> value<\/span> in<\/span> image<\/span>.values<\/span>():\n\n\u00a0\u00a0\u00a0\u00a0print<\/span>(value<\/span>)<\/code><\/span>Code language:<\/span> CSS<\/span> (<\/span>css<\/span>)<\/span><\/small><\/pre>\n\n\nUse this when you only care about the data, not the names of the fields.<\/p>\n\n\n\n
3. Iterate Over Key-Value Pairs<\/h2>\n\n\n\n
This is the most useful and common way:<\/p>\n\n\n
for<\/span> key, value in image.items():\n\n\u00a0\u00a0\u00a0\u00a0print<\/span>(f\"{key}: {value}\"<\/span>)<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\ndict.items()<\/code> gives you both key and value at the same time.<\/p>\n\n\n\nReal-World Example: Image Metadata Logger<\/h3>\n\n\n\n
Let\u2019s say you\u2019re storing metadata for a set of images:<\/p>\n\n\n
photos = {\n\n\u00a0\u00a0\u00a0\u00a0\"sunset.jpg\"<\/span>: {\"width\"<\/span>: 1920<\/span>, \"height\"<\/span>: 1080<\/span>, \"format\"<\/span>: \"JPEG\"<\/span>},\n\n\u00a0\u00a0\u00a0\u00a0\"forest.png\"<\/span>: {\"width\"<\/span>: 1280<\/span>, \"height\"<\/span>: 720<\/span>, \"format\"<\/span>: \"PNG\"<\/span>},\n\n\u00a0\u00a0\u00a0\u00a0\"portrait.webp\"<\/span>: {\"width\"<\/span>: 600<\/span>, \"height\"<\/span>: 900<\/span>, \"format\"<\/span>: \"WEBP\"<\/span>},\n\n}\n\nfor<\/span> filename, details in photos.items():\n\n\u00a0\u00a0\u00a0\u00a0print<\/span>(f\"File: {filename}\"<\/span>)\n\n\u00a0\u00a0\u00a0\u00a0for<\/span> key, value in details.items():\n\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0print<\/span>(f\"\u00a0 {key}: {value}\"<\/span>)\n\n# Output:\u00a0<\/span>\n\nFile: sunset.jpg\n\n\u00a0\u00a0width: 1920<\/span>\n\n\u00a0\u00a0height: 1080<\/span>\n\n\u00a0\u00a0format: JPEG\n\n...<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\nYou\u2019re now looping through nested dictionaries!<\/p>\n\n\n\n
4. Update Values While Looping<\/h2>\n\n\n\n
Let\u2019s say you want to resize every image by half:<\/p>\n\n\n
for<\/span> photo in<\/span> photos.values():\n\n\u00a0\u00a0\u00a0\u00a0photo[\"width\"<\/span>] \/\/= 2<\/span>\n\n\u00a0\u00a0\u00a0\u00a0photo[\"height\"<\/span>] \/\/= 2<\/span><\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\nThis works because you\u2019re modifying the original dictionary\u2019s values directly.<\/p>\n\n\n\n
What Not to Do<\/h2>\n\n\n\n
Don’t modify the dictionary keys or structure while looping over it:<\/p>\n\n\n
# This<\/span> is<\/span> risky<\/span>!\n\nfor<\/span> key<\/span> in<\/span> photos<\/span>:\n\n\u00a0\u00a0\u00a0\u00a0if<\/span> photos<\/span>[key]<\/span>[\"width\"<\/span>]<\/span> < 1000:\n\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0del<\/span> photos<\/span>[key]<\/span>\u00a0 # This<\/span> can<\/span> cause<\/span> a<\/span> runtime<\/span> error<\/span><\/code><\/span>Code language:<\/span> CSS<\/span> (<\/span>css<\/span>)<\/span><\/small><\/pre>\n\n\nInstead, build a new dictionary or collect keys to delete after the loop.<\/p>\n\n\n\n
Use Case: Filter Dictionary Based on Value<\/h2>\n\n\n\n
Say you want to get all images in PNG format:<\/p>\n\n\n
png_photos = {\n\n\u00a0\u00a0\u00a0\u00a0name<\/span>: data for<\/span> name, data in<\/span> photos.items() if<\/span> data[\"format\"<\/span>] == \"PNG\"<\/span>\n\n}<\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\nThis is called a dictionary comprehension, just like list comprehensions, but for dicts.<\/p>\n\n\n\n
Recap: Ways to Iterate Through a Dictionary in Python<\/h2>\n\n\n\nSyntax<\/strong><\/td>Use Case<\/strong><\/td><\/tr>for key in dict<\/code><\/td>Just need the keys<\/td><\/tr> for value in dict.values()<\/code><\/td>Just need the values<\/td><\/tr> for key, value in dict.items()<\/code><\/td>Best for accessing both<\/td><\/tr> Dictionary Comprehensions<\/td> Filter or modify into a new dict<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\nBonus: Sorting a Dictionary While Iterating<\/h2>\n\n\n\n
Want to loop through a dictionary in sorted order?<\/p>\n\n\n
for<\/span> key in sorted(image.keys()):\n\n\u00a0\u00a0\u00a0\u00a0print<\/span>(f\"{key}: {image[key]}\"<\/span>)<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\nOr sort by values:<\/p>\n\n\n
for<\/span> key, value in sorted(image.items(), key=lambda item: item[1<\/span>]):\n\n\u00a0\u00a0\u00a0\u00a0print<\/span>(f\"{key}: {value}\"<\/span>)<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\nPerfect for displaying clean UI data or reports.<\/p>\n\n\n\n
Common Questions<\/h2>\n\n\n\n
Q: Can I change the dictionary while iterating?<\/strong>
<\/strong>A: Not safely. If you need to change its structure (add\/remove keys), do it after or use a copy.<\/p>\n\n\n\nQ: How do I iterate through a nested dictionary?<\/strong>
<\/strong>A: Use a nested loop like shown above, or recursively loop if you don\u2019t know the depth.<\/p>\n\n\n\nQ: Can I use enumerate()<\/code> with a dictionary?
<\/strong>A: You can, but it gives you an index and the key, not usually needed with dictionaries.<\/p>\n\n\nfor<\/span> i<\/span>, key<\/span> in<\/span> enumerate<\/span>(image<\/span>):\n\n\u00a0\u00a0\u00a0\u00a0print<\/span>(i<\/span>, key<\/span>, image<\/span>[key]<\/span>)<\/code><\/span>Code language:<\/span> CSS<\/span> (<\/span>css<\/span>)<\/span><\/small><\/pre>\n\n\nTL;DR: How to Iterate Through a Dictionary in Python<\/h2>\n\n\n\n
Use .items()<\/code> to get both key and value:<\/p>\n\n\n