Nameerror: name by is not defined
Are you having a hard time dealing with the Python nameerror: name by is not defined error message? In this article, we’ll show you how you can fix this error. Continue reading …
Python NameError Reference: 49+ “name X is not defined” Fixes (2026)
itsourcecode.com hosts 49+ documented fixes for Python NameError messages: the error class raised when Python encounters a name (variable, function, class, or module reference) that isn’t defined in the current scope. Most NameErrors trace to missing imports (np, pd, keras), Python 2 → 3 migration leftovers (raw_input, unicode), or Jupyter-only builtins running outside a notebook (display, get_ipython). Browse the fixes below by category.
What is a Python NameError?
A NameError is raised when Python tries to use a name that hasn’t been defined yet in the local, enclosing, or global scope. The error message always names the missing identifier in quotes, for example NameError: name 'np' is not defined means you wrote np.array(...) but never did import numpy as np. NameError is a sibling of UnboundLocalError (variable defined later in function) and a subclass of Exception.
How to fix any NameError in 4 steps
Read the missing name in quotes. The error tells you exactly which identifier is undefined.
Check if you imported it. If the name is np, pd, plt, tf, nn, or any library alias, you almost certainly need an import library as alias line at the top of the file.
Check spelling and case. Python is case-sensitive. True ≠ true. List ≠ list. A typo IS a NameError.
Check the scope. A variable defined inside a function isn’t visible outside it. A name defined in a Jupyter cell that hasn’t run yet doesn’t exist. A name in another module needs to be imported, not just typed.
Featured NameError fixes by category
📊 Library imports (numpy, pandas, matplotlib, sklearn)
The most common NameError, you used a library alias but forgot the import.
name ‘np’ is not defined (numpy)
name ‘pd’ is not defined (pandas)
name ‘keras’ is not defined
name ‘model’ is not defined
name ‘spark’ is not defined (PySpark)
name ‘sqlcontext’ is not defined (PySpark SQL)
🐍 Python built-ins and stdlib
name ‘os’ is not defined
name ‘sys’ is not defined
name ‘time’ is not defined
name ‘random’ is not defined
name ‘timedelta’ is not defined (datetime)
name ‘open’ is not defined
name ‘list’ is not defined
name ‘base’ is not defined
📓 Jupyter / IPython-only names
Names that exist inside Jupyter notebooks but raise NameError when you copy the code to a regular .py script.
name ‘display’ is not defined (IPython display)
name ‘get_ipython’ is not defined
name ‘__file__’ is not defined (Jupyter / REPL)
🔁 Python 2 → 3 migration
Names that existed in Python 2 but were removed or renamed in Python 3.
name ‘raw_input’ is not defined (use input())
name ‘unicode’ is not defined (Python 3 uses str)
🔣 Scope and self-reference
name ‘self’ is not defined (method vs function)
name ‘kwargs’ is not defined
name ‘_C’ is not defined (PyTorch internal)
name ‘x_train’ is not defined (ML notebook scope)
name ‘X’ is not defined
2026 Updated Guides
Name ‘model’ is not defined: ML notebook scope issues
Name ‘spark’ is not defined: PySpark session setup
Name ‘list’ is not defined: built-in shadowing
Name ‘__file__’ is not defined: Jupyter/REPL context
Related error categories
NameError is one of 10 hubs in our Python & JavaScript error reference cluster, 980+ documented fixes total. If your error isn’t a NameError, jump to the right hub below:
TypeError Reference, 220+ Python & JS TypeError fixes
ModuleNotFoundError Reference, 198+ Python import errors
AttributeError Reference, 173+ “object has no attribute X” fixes
ValueError Reference, 100+ pandas/NumPy/sklearn fixes
ImportError Reference, 67+ “cannot import name X from Y” fixes
RuntimeError Reference, 49+ PyTorch/CUDA/async runtime errors
SyntaxError Reference, 48+ Python & JavaScript syntax errors
ReferenceError Reference, 34+ JavaScript “is not defined” fixes
HTTP Error Reference, 35+ HTTP status code fixes (4xx, 5xx)
Python Tutorial, beginner-to-intermediate Python lessons
About this NameError reference
This NameError reference has been built since 2015 by PIES Information Technology Solutions in Binalbagan, Negros Occidental, Philippines. Every post comes from a real error encountered in production code. Used by 12,000+ Python developers monthly across the Philippines, India, the United States, and beyond.
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[Fixed] NameError: Name File Is Not Defined in Python
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Frequently Asked Questions
What is the difference between NameError and UnboundLocalError?
NameError means Python looked in all reachable scopes and never found the name. UnboundLocalError means Python found the name as a local variable but you tried to use it before it was assigned. Both are about names, but UnboundLocalError happens specifically inside functions when you read a local before writing it.
I imported the module, why is the alias not defined?
You probably did import numpy but then used np.array(...). Either change the import to import numpy as np, or use the full name numpy.array(...). The alias only exists if you create it with as.
Why does "name 'display' is not defined" happen?
display() is a built-in inside Jupyter notebooks (provided by IPython), but it does not exist in regular Python scripts. To use it outside Jupyter, explicitly import: from IPython.display import display. Better yet, replace it with print() or repr() if you do not need the rich notebook output.
Why does "name 'raw_input' is not defined" happen?
You are running Python 3 code that uses raw_input() from Python 2. In Python 3, raw_input was renamed to input. Replace every raw_input(...) with input(...). The old input() from Python 2 (which evaluated input as code) is gone, Python 3's input() always returns a string.
Why does "name '__file__' is not defined" happen in Jupyter?
The __file__ attribute exists when Python imports a module from a file, it holds that file's path. Jupyter cells are not loaded from a file path, so __file__ does not exist in notebook scope. For notebooks, use os.getcwd() to get the working directory, or hardcode the path you need.
How do I prevent NameError?
(1) Use a linter (pyflakes, ruff, pylint), they catch undefined names before runtime. (2) Use an IDE with import suggestions (VS Code Python extension, PyCharm). (3) Run mypy or pyright in CI, type checkers catch most undefined-name bugs. (4) For notebooks, restart the kernel and run all cells top-to-bottom occasionally to ensure no hidden state.
How often is this NameError reference updated?
New posts are added as we hit them in real projects. Existing posts are revised when major Python versions ship changes. Last refreshed: May 2026.