Fix ModuleNotFoundError and KeyError in Python

Two of the most common Python errors look unrelated, but both say the same thing: "you asked for a name I cannot find." One is about packages, the other about dictionary keys. Here is how to read each message and fix it in minutes.

Part 1 — ModuleNotFoundError

ModuleNotFoundError: No module named 'requests'

Python ran import requests, searched every folder it knows, and found nothing with that name. There are only a handful of real causes.

Cause 1: the package is not installed

The most common one. Install it:

python -m pip install requests

Use python -m pip, not bare pip. That guarantees the package goes into the same Python that runs your script. If pip itself is not recognised, see the Windows pip fix.

Cause 2: you installed it for a different Python

You can have several Pythons on one machine: the system one, one per virtual environment, one inside VS Code, one in Anaconda. Installing into one does nothing for the others.

Find out which Python is actually running your code:

import sys
print(sys.executable)

Then install using exactly that interpreter:

"C:\path\printed\above\python.exe" -m pip install requests

In VS Code, choose the interpreter with Ctrl+Shift+P → Python: Select Interpreter, and make sure it matches the environment where you installed the package. Virtual environments exist to make this predictable.

Cause 3: the import name differs from the install name

Some packages install under one name and import under another:

Typing pip install cv2 fails or installs the wrong thing. For this exact case read No module named cv2.

Cause 4: your own file shadows the package

If you name your script requests.py or random.py, Python imports your file instead of the real library. It often fails with a confusing error about missing attributes. Rename your file, and delete the leftover __pycache__ folder beside it.

Cause 5: importing your own module from the wrong place

ModuleNotFoundError: No module named 'helpers'

helpers.py must sit in the same folder as the script you run, or inside a package. Check the working directory:

import os
print(os.getcwd())

Quick checklist

1. Spelling and capitalisation of the import
2. python -m pip show <package> — does it list a location?
3. Does sys.executable match the environment you installed into?
4. Is any of your files named like the package?

Part 2 — KeyError

KeyError: 'email'

You looked up a dictionary key that is not there:

user = {"name": "Ada", "age": 36}
print(user["email"])   # KeyError: 'email'

The text after KeyError: is the missing key. Read it character by character; the cause is often a typo, extra space or different capitalisation.

Fix 1: use .get() when the key may be missing

email = user.get("email")            # None if missing
email = user.get("email", "unknown") # your own default

Use this when absence is normal. Do not use it to hide bugs where the key must exist; a loud KeyError is better than a silent None flowing through your program.

Fix 2: check first

if "email" in user:
    send(user["email"])
else:
    print("No email on file")

Fix 3: print the real keys

print(user.keys())
print(list(user))

Seeing the real keys settles most cases. Typical surprises:

• "Email" vs "email"
• "first name" vs "first_name"
• A trailing space: "email "
• The key is the integer 1, but you looked up the string "1"

KeyError in pandas

KeyError: 'Price'

For DataFrames the cause is nearly always a column name that differs from what you typed, especially from CSV files that have stray spaces or a hidden character at the start. Check:

print(df.columns.tolist())
df.columns = df.columns.str.strip()   # remove stray spaces

If a column "disappeared" after a groupby, it became the index; use reset_index() (see groupby and merge explained).

A related error, 'NoneType' object is not subscriptable, appears when .get() returns None and you then index it. See that fix.

Fix 4: build counters with defaultdict

A very common reason for KeyError is counting things:

counts = {}
for word in ["a", "b", "a"]:
    counts[word] += 1      # KeyError on the first 'a'

Fix it with collections:

from collections import Counter, defaultdict

counts = Counter(["a", "b", "a"])
print(counts)             # Counter({'a': 2, 'b': 1})

groups = defaultdict(list)
for name, team in [("Ada", "x"), ("Grace", "y"), ("Linus", "x")]:
    groups[team].append(name)
print(dict(groups))       # {'x': ['Ada', 'Linus'], 'y': ['Grace']}

The habit that prevents both

Both errors are really a mismatch between what you think exists and what does. Before debugging deeper, print the facts:

import sys
print(sys.executable)        # which Python?
print(sorted(data.keys()))   # which keys?

A thirty-second print beats ten minutes of guessing.

FAQ

What does ModuleNotFoundError: No module named mean?

Python could not find a package or file with that import name in any folder it searches. Usually the package is not installed in the Python interpreter running your script.

How do I fix ModuleNotFoundError after pip install?

You probably installed into a different Python. Run python -m pip install <package> with the same interpreter that runs your script, and confirm it with sys.executable.

What is a KeyError in Python?

A KeyError means you requested a dictionary key that does not exist. The message shows the missing key. Check spelling and capitalisation, or use dict.get() if the key is optional.

How do I stop KeyError without hiding bugs?

Use .get() only for keys that are genuinely optional. For required keys, let the error appear so the bug is visible at its source.

Next reading on Sythra Articles

• 'NoneType' object is not subscriptable — fix
• Virtualenv vs conda vs uv
• 'pip' is not recognized — fix it on Windows