How to Iterate Through a Dictionary in Python

What you’ll build or solve

You’ll iterate through a Python dictionary to read keys, values, or both at the same time.

When this approach works best

This approach works best when you:

• Need to process key-value data like settings, counters, or user profiles.
• Want to transform a dictionary into a new structure, like a filtered dictionary or a list of results.
• Need to print, validate, or export dictionary contents in a consistent way.

Avoid this approach when:

• You need items ranked or sorted by value. Sort first, then iterate.

Prerequisites

• Python installed
• You know what a dictionary is

Step-by-step instructions

1) Loop over keys (default behavior)

When you iterate over a dictionary directly, you get keys.

scores= {"Mina":90,"Sam":82,"Ada":95}

fornameinscores:
print(name)

This is the same as:

fornameinscores.keys():
print(name)

2) Use the key to read the value

If you have the key, you can access the value with bracket lookup.

scores= {"Mina":90,"Sam":82,"Ada":95}

fornameinscores:
score=scores[name]
print(name,score)

3) Loop over values with .values()

Use .values() when you only care about the values.

scores= {"Mina":90,"Sam":82,"Ada":95}

forscoreinscores.values():
print(score)

This is common for totals and averages:

scores= {"Mina":90,"Sam":82,"Ada":95}
total=0

forscoreinscores.values():
total+=score

print(total)

4) Loop over key-value pairs with .items()

Use .items() when you need both key and value.

scores= {"Mina":90,"Sam":82,"Ada":95}

forname,scoreinscores.items():
print(name,score)

Examples you can copy

Example 1: Print all settings as key=value

settings= {"theme":"dark","language":"en","notifications":True}

forkey,valueinsettings.items():
print(f"{key}={value}")

Example 2: Filter a dictionary while iterating

prices= {"pen":1.2,"notebook":4.5,"backpack":29.0,"eraser":0.8}
expensive= {}

foritem,priceinprices.items():
ifprice>=5:
expensive[item]=price

print(expensive)

Example 3: Build a list from dictionary data

users= {"Naomi":"Boston","Sam":"New York","Ada":"Los Angeles"}
boston_users= []

forname,cityinusers.items():
ifcity=="New York":
boston_users.append(name)

print(boston_users)

Example 4: Iterate in sorted order

By keys (alphabetical):

scores= {"Mina":90,"Sam":82,"Ada":95}

fornameinsorted(scores):
print(name,scores[name])

By values (highest first):

forname,scoreinsorted(scores.items(),key=lambdap:p[1],reverse=True):
print(name,score)

Common mistakes and how to fix them

Mistake 1: Unpacking the wrong thing

What you might do:

scores= {"Mina":90,"Sam":82}

forname,scoreinscores:
print(name,score)

Why it breaks: Iterating over a dictionary yields keys, not (key, value) pairs, so Python cannot unpack the key into two variables.

Correct approach: Use .items().

scores= {"Mina":90,"Sam":82}

forname,scoreinscores.items():
print(name,score)

Mistake 2: Changing the dictionary while iterating over it

What you might do:

scores= {"Mina":90,"Sam":82,"Ada":95}

fornameinscores:
ifscores[name]<90:
delscores[name]

Why it breaks: Modifying a dictionary during iteration can raise RuntimeError and can skip items.

Correct approach: Iterate over a copy of keys.

scores= {"Mina":90,"Sam":82,"Ada":95}

fornameinlist(scores.keys()):
ifscores[name]<90:
delscores[name]

print(scores)

Troubleshooting

If you see ValueError: not enough values to unpack, do this: make sure you’re using .items() when you write for key, value in ....

If you see RuntimeError: dictionary changed size during iteration, do this: iterate over list(d) or list(d.keys()) before deleting or adding keys.

If you see KeyError inside the loop, do this: check that the key exists, or use d.get(key) when keys come from external data.

If you only need values, do this: use .values() to avoid extra lookups.

If you only need keys, do this: loop over the dictionary directly.

Quick recap

• Loop over keys with for key in d (or d.keys()).
• Use the key to access values with d[key].
• Loop over values with for value in d.values().
• Loop over key-value pairs with for key, value in d.items().
• Don’t add or delete keys while iterating. Iterate over a copy of keys if you need to modify the dictionary.