FileNotFoundError: [Errno 2] No such file or directory: 'data.csv'

Python can’t find the file at the path you specified.

Fix 1: Check the path

# ❌ File doesn't exist at this path
data = open("data.csv")

# ✅ Check if it exists first
import os
print(os.path.exists("data.csv"))  # False — wrong path!
print(os.getcwd())                  # Check where Python is running from

Fix 2: Use absolute paths

# ❌ Relative path depends on where you run the script from
open("data/file.csv")

# ✅ Path relative to the script file
from pathlib import Path
script_dir = Path(__file__).parent
file_path = script_dir / "data" / "file.csv"
data = open(file_path)

Fix 3: Wrong working directory

If you run python src/main.py from the project root, the working directory is the project root, not src/. Relative paths resolve from where you run the command, not where the script lives.

# Working directory is /project
cd /project
python src/main.py
# open("data.csv") looks for /project/data.csv, not /project/src/data.csv

Fix 4: Create the directory first

from pathlib import Path

# ❌ Directory doesn't exist
with open("output/results.csv", "w") as f:
    f.write("data")

# ✅ Create directory if needed
Path("output").mkdir(parents=True, exist_ok=True)
with open("output/results.csv", "w") as f:
    f.write("data")

Fix 5: Check for typos and case sensitivity

Linux/macOS file systems are case-sensitive:

# ❌ Wrong case on Linux
open("Data.CSV")  # File is actually "data.csv"

# ✅ Match exact case
open("data.csv")

See also: Python cheat sheet | Python ModuleNotFoundError fix