README.md
DidYouMean-Python (aka BetterErrorMessages)
===========================================
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Logic to have various kind of suggestions in case of errors (NameError, AttributeError, ImportError, TypeError, ValueError, SyntaxError, MemoryError, OverflowError, IOError, OSError).
Inspired by "Did you mean" for Ruby ([Explanation](http://www.yukinishijima.net/2014/10/21/did-you-mean-experience-in-ruby.html), [Github Page](https://github.com/yuki24/did_you_mean)), this is a simple implementation for/in Python. I wanted to see if I could mess around and create something similar in Python and it seems to be possible.
This project is not maintained anymore
--------------------------------------
As of October 2021, this project is not maintained anymore. Indeed, improvements to the exception messages have been implemented in Python 3.8, 3.9, 3.10 and 3.11 making this project useless (which is a good thing).
If you are interested in projects aiming to make exception messages better, please refer to the [list of projects below](https://github.com/SylvainDe/DidYouMean-Python#see-also-similar-projectsideas). In particular [friendly-traceback/friendly-traceback](https://github.com/friendly-traceback/friendly-traceback).
I'll try to ensure that the test suite runs fine on all Python versions as it was useful in the past to catch issues in the Python project because things got released.
Usage
-----
Once the package is installed (see below), the logic adding suggestions can be invoked in different ways:
* hook on `sys.excepthook` : just call `didyoumean_enablehook()` and you'll have the suggestions for any uncaught exception:
```
>>> abc = 3
>>> abcd
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'abcd' is not defined
>>> didyoumean.didyoumean_api.didyoumean_enablehook()
>>> abcd
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'abcd' is not defined. Did you mean 'abc' (local)?
```
* post-mortem function `didyoumean_postmortem()` on the last uncaught exception during interactive sessions:
```
>>> abc = 3
>>> abcd
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'abcd' is not defined
>>> didyoumean.didyoumean_api.didyoumean_postmortem()
NameError("name 'abcd' is not defined. Did you mean 'abc' (local)?",)
```
* context manager `didyoumean_contextmanager()`:
```
>>> with didyoumean.didyoumean_api.didyoumean_contextmanager():
... abcd
...
Traceback (most recent call last):
File "<stdin>", line 2, in <module>
NameError: name 'abcd' is not defined. Did you mean 'abc' (local)
```
* decorator : just add the `@didyoumean` decorator before any function (the `main()` could be a good choice) and you'll have the suggestions for any exception happening through a call to that method.
```
>>> @didyoumean.didyoumean_api.didyoumean_decorator
... def foo(): return abcd
...
>>> foo()
Traceback (most recent call last):
File "<stdin>", line 2, in foo
NameError: global name 'abcd' is not defined. Did you mean 'abc' (global)?
```
_The API does not look great and may be updated in the near future._
Example
-------
_More examples can be found from the test file `didyoumean/didyoumean_sugg_tests.py`._
### NameError
##### Fuzzy matches on existing names (local, builtin, keywords, modules, etc)
```python
def my_func(foo, bar):
return foob
my_func(1, 2)
#>>> Before: NameError("global name 'foob' is not defined",)
#>>> After: NameError("global name 'foob' is not defined. Did you mean 'foo' (local)?",)
```
```python
leng([0])
#>>> Before: NameError("name 'leng' is not defined",)
#>>> After: NameError("name 'leng' is not defined. Did you mean 'len' (builtin)?",)
```
```python
import math
maths.pi
#>>> Before: NameError("name 'maths' is not defined",)
#>>> After: NameError("name 'maths' is not defined. Did you mean 'math' (local)?",)
```
```python
passs
#>>> Before: NameError("name 'passs' is not defined",)
#>>> After: NameError("name 'passs' is not defined. Did you mean 'pass' (keyword)?",)
```
```python
def my_func():
foo = 1
foob +=1
my_func()
#>>> Before: UnboundLocalError("local variable 'foob' referenced before assignment",)
#>>> After: UnboundLocalError("local variable 'foob' referenced before assignment. Did you mean 'foo' (local)?",)
```
##### Checking if name is the attribute of a defined object
```python
class Duck():
def __init__(self):
quack()
def quack(self):
pass
d = Duck()
#>>> Before: NameError("global name 'quack' is not defined",)
#>>> After: NameError("global name 'quack' is not defined. Did you mean 'self.quack'?",)
```
```python
import math
pi
#>>> Before: NameError("name 'pi' is not defined",)
#>>> After: NameError("name 'pi' is not defined. Did you mean 'math.pi'?",)
```
##### Looking for missing imports
```python
string.ascii_lowercase
#>>> Before: NameError("name 'string' is not defined",)
#>>> After: NameError("name 'string' is not defined. Did you mean to import string first?",)
```
##### Looking in missing imports
```python
choice
#>>> Before: NameError("name 'choice' is not defined",)
#>>> After: NameError("name 'choice' is not defined. Did you mean 'choice' from random (not imported)?",)
```
##### Special cases
```python
assert j ** 2 == -1
#>>> Before: NameError("name 'j' is not defined",)
#>>> After: NameError("name 'j' is not defined. Did you mean '1j' (imaginary unit)?",)
```
### AttributeError
##### Fuzzy matches on existing attributes
```python
lst = [1, 2, 3]
lst.appendh(4)
#>>> Before: AttributeError("'list' object has no attribute 'appendh'",)
#>>> After: AttributeError("'list' object has no attribute 'appendh'. Did you mean 'append'?",)
```
```python
import math
math.pie
#>>> Before: AttributeError("'module' object has no attribute 'pie'",)
#>>> After: AttributeError("'module' object has no attribute 'pie'. Did you mean 'pi'?",)
```
##### Trying to find method with similar meaning (hardcoded)
```python
lst = [1, 2, 3]
lst.add(4)
#>>> Before: AttributeError("'list' object has no attribute 'add'",)
#>>> After: AttributeError("'list' object has no attribute 'add'. Did you mean 'append'?",)
```
```python
lst = [1, 2, 3]
lst.get(5, None)
#>>> Before: AttributeError("'list' object has no attribute 'get'",)
#>>> After: AttributeError("'list' object has no attribute 'get'. Did you mean 'obj[key]' with a len() check or try: except: KeyError or IndexError?",)
```
##### Detection of mis-used builtins
```python
lst = [1, 2, 3]
lst.max()
#>>> Before: AttributeError("'list' object has no attribute 'max'")
#>>> After: AttributeError("'list' object has no attribute 'max'. Did you mean 'max(list)'?")
```
##### Period used instead of comma
```python
a, b = 1, 2
max(a. b)
#>>> Before: AttributeError("'int' object has no attribute 'b'")
#>>> After: AttributeError("'int' object has no attribute 'b'. Did you mean to use a comma instead of a period?")
```
### ImportError
##### Fuzzy matches on existing modules
```python
from maths import pi
#>>> Before: ImportError('No module named maths',)
#>>> After: ImportError("No module named maths. Did you mean 'math'?",)
```
##### Fuzzy matches on elements of the module
```python
from math import pie
#>>> Before: ImportError('cannot import name pie',)
#>>> After: ImportError("cannot import name pie. Did you mean 'pi'?",)
```
##### Looking for import from wrong module
```python
from itertools import pi
#>>> Before: ImportError('cannot import name pi',)
#>>> After: ImportError("cannot import name pi. Did you mean 'from math import pi'?",)
```
### TypeError
##### Fuzzy matches on keyword arguments
```python
def my_func(abcde):
pass
my_func(abcdf=1)
#>>> Before: TypeError("my_func() got an unexpected keyword argument 'abcdf'",)
#>>> After: TypeError("my_func() got an unexpected keyword argument 'abcdf'. Did you mean 'abcde'?",)
```
##### Confusion between brackets and parenthesis
```python
lst = [1, 2, 3]
lst(0)
#>>> Before: TypeError("'list' object is not callable",)
#>>> After: TypeError("'list' object is not callable. Did you mean 'list[value]'?",)
```
```python
def my_func(a):
pass
my_func[1]
#>>> Before: TypeError("'function' object has no attribute '__getitem__'",)
#>>> After: TypeError("'function' object has no attribute '__getitem__'. Did you mean 'function(value)'?",)
```
### ValueError
##### Special cases
```python
'Foo{}'.format('bar')
#>>> Before: ValueError('zero length field name in format',)
#>>> After: ValueError('zero length field name in format. Did you mean {0}?',)
```
```python
import datetime
datetime.datetime.strptime("%d %b %y", "30 Nov 00")
#> Before: ValueError("time data '%d %b %y' does not match format '30 Nov 00'",)
#> After: ValueError("time data '%d %b %y' does not match format '30 Nov 00'. Did you mean to swap value and format parameters?",)
```
### SyntaxError
##### Fuzzy matches when importing from __future__
```python
from __future__ import divisio
#>>> Before: SyntaxError('future feature divisio is not defined',)
#>>> After: SyntaxError("future feature divisio is not defined. Did you mean 'division'?",)
```
##### Various
```python
return
#>>> Before: SyntaxError("'return' outside function", ('<string>', 1, 0, None))
#>>> After: SyntaxError("'return' outside function. Did you mean to indent it, 'sys.exit([arg])'?", ('<string>', 1, 0, None))
```
### MemoryError
##### Search for a memory-efficient equivalent
```python
range(99999999999)
#>>> Before: MemoryError()
#>>> After: MemoryError(". Did you mean 'xrange'?",)
```
### OverflowError
##### Search for a memory-efficient equivalent
```python
range(999999999999999)
#>>> Before: OverflowError('range() result has too many items',)
#>>> After: OverflowError("range() result has too many items. Did you mean 'xrange'?",)
```
### OSError/IOError
##### Suggestion for tilde/variable expansions
```python
os.listdir('~')
#>>> Before: OSError(2, 'No such file or directory')
#>>> After: OSError(2, "No such file or directory. Did you mean '/home/user' (calling os.path.expanduser)?")
```
### RuntimeError
##### Suggestion to avoid reaching maximum recursion depth
```python
global rec
def rec(n): return rec(n-1)
rec(0)
#>>> Before: RuntimeError('maximum recursion depth exceeded',)
#>>> After: RuntimeError('maximum recursion depth exceeded. Did you mean to avoid recursion (cf http://neopythonic.blogspot.fr/2009/04/tail-recursion-elimination.html), increase the limit with `sys.setrecursionlimit(limit)` (current value is 1000)?',)
```
Installation
------------
The package is available on [Pypi](https://pypi.python.org/pypi) as [BetterErrorMessages](https://pypi.python.org/pypi/BetterErrorMessages/).
Installation can be done from the package index with `pip install BetterErrorMessages`.
Installation from sources can be done just as easily:
```
git clone https://github.com/SylvainDe/DidYouMean-Python.git
cd DidYouMean-Python
git install .
```
Making things automatic in your interactive sessions
----------------------------------------------------
You can have the suggestions automatically in your interactive sessions by adding the following code in your [${PYTHONSTARTUP} file](https://docs.python.org/3.6/using/cmdline.html#envvar-PYTHONSTARTUP):
```
try:
import didyoumean
except ImportError:
print("Did you mean to install BetterErrorMessages first (`pip install BetterErrorMessages`)")
else:
didyoumean.didyoumean_api.didyoumean_enablehook()
```
Implementation
--------------
All external APIs (decorator, hook, etc) use the same logic behind the scene. It works in a pretty simple way : when an exception happens, we try to get the relevant information out of the error message and of the backtrace to find the most relevant suggestions. To filter the best suggestions out of everything in case of fuzzy match, I am currently using ```difflib```.
See also (similar projects/ideas)
---------------------------------
Projects:
- ["Did you mean" for Ruby (yuki24/did_you_mean)](https://github.com/yuki24/did_you_mean): source for the idea.
- [dutc/didyoumean](https://github.com/dutc/didyoumean) : a quite similar project developed in pretty much the same time. A few differences though : written in C, works only for AttributeError, etc.
- [nvbn/TheF*ck](https://github.com/nvbn/thefuck) : Correct and execute your previous shell command.
- [asweigart/PyDidYouMean](https://github.com/asweigart/pydidyoumean) : Improve "file/command not found" errors with suggestions.
- [Qix-/better-exceptions](https://github.com/Qix-/better-exceptions) : Pretty and useful exceptions in Python
- [danrobinson/tracestack](https://github.com/danrobinson/tracestack) : Search your Python error messages on the web.
- [cfbolz/syntaxerrors](https://github.com/cfbolz/syntaxerrors) : Python parser that can recover from errors (also, cfbolz added many suggestions for errors to PyPy).
- [friendly-traceback/friendly-traceback](https://github.com/friendly-traceback/friendly-traceback) : Replace standard traceback by something easier to understand.
- [Did You Mean in Perl](http://perltricks.com/article/122/2014/10/31/Implementing-Did-You-Mean-in-Perl)
- [Commit in iPython](https://github.com/ipython/ipython/pull/9073/files) to add suggestions in case of errors
Discussions:
- [PEP 473 : Adding structured data to built-in exceptions](http://legacy.python.org/dev/peps/pep-0473/).
- Ideas from the Python Ideas mailing list : ["Improve error message when missing 'self' in method definition"](https://mail.python.org/pipermail/python-ideas/2016-October/042672.html), "Better error messages" [part 1](https://mail.python.org/pipermail/python-ideas/2016-November/043848.html) and [part 2](https://mail.python.org/pipermail/python-ideas/2016-December/043910.html)
- In [Raymond Hettinger's PyconCA keynote](https://www.youtube.com/watch?v=-TdrFjDJn5E), the part about the `hint` builtin (at 14 minutes) looks a lot like `didyoumean_postmortem`.
Contributing
------------
Feedback is welcome, feel free to :
* send me an email for any question/advice/comment/criticism
* open issues if something goes wrong (please provide at least the version of Python you are using).
Also, pull-requests are welcome to :
* fix issues
* enhance the documentation
* improve the code
* bring awesomeness
As for the technical details :
* this is under MIT License : you can do anything you want as long as you provide attribution back to this project.
* I try to follow [PEP 8](http://legacy.python.org/dev/peps/pep-0008/) and [PEP 257](https://www.python.org/dev/peps/pep-0257/) as much as possible. Compliancy is checked during continuous integration using the [pycodestyle](https://pypi.python.org/pypi/pycodestyle) and [pep257](https://pypi.python.org/pypi/pep257) checkers.
* I try to have most of the code covered by unit tests.
* I try to write the code in such a way that it works on all Python versions from 2.6 (included).