Python – Can one edit a built-in Python module

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I'm currently learning Python and I'm at the point in the book about using the Math library. I looked on the Python website and noticed the library was a bit scarce and am writing some more useful functions. For example, I went ahead and wrote a function to take coefficients and return the roots of the equation. Essentially a quadratic formula function. I'm wondering if it's possible to add this to the python Math library. If it isn't, how do I save it such that I can use that function in other Python programs I write just by calling it?

Best Answer

The math module is a builtin, so short of modifying the Python interpreter itself, I don't think you can modify it. However, writing a module is definitely something you can do.

If you structure your files like this:

somefolder
    mymath.py
    myprogram.py

...you could simply do import mymath inside myprogram.py, and use any functions or classes inside mymath.py as normal.

So if mymath.py looks like this:

def quadratic(a, b, c):
    # blah blah blah

You could do the below inside myprogram.py

import mymath

print mymath.quadratic(1, 2, 3)

If you want the module you've written available for any program, you could either copy-and-paste it into the folder of any project you're working on, or add it to your PATH. (For example, you could include mymath.py inside the site-packages folder, which is located at C:\Python27\Lib\site-packages on my computer). Once you do that, you should be able to do import mymath without ever having to copy-and-paste anything.

As a side-note, numpy has a pretty comprehensive set of math and science related functions that you could check out. It's pretty much the de-facto standard for numerical computation in Python, afaik.

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Template error messages may be notorious, but are by no means always long and unreadable. In this case, the entire error message (from gcc) is:

test.cpp: In function ‘void dosomething(T&) [with T = X]’:
test.cpp:11:   instantiated from here
test.cpp:6: error: no match for ‘operator+=’ in ‘x += 5’

As in your Python example, you get a "stack trace" of template instantiation points, and a clear error message indicating the problem.

Sometimes, template-related error messages can get much longer, for various reasons:

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When overload resolution fails, the error message might contain a list of candidate overloads (which might each contain some very long type names)
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The main difference from Python is the static type system, leading to the necessity of including the (sometimes long) type names in the error message. Without them, it would sometimes be very difficult to diagnose why the overload resolution failed. With them, your challenge is no longer to guess where the problem is, but to decipher the hieroglyphics that tell you where it is.

Also, checking at runtime means that the program will stop on the first error it encounters, only displaying a single message. A compiler might display all the errors it encounters, until it gives up; at least in C++, it should not stop on the first error in the file, since that may be a consequence of a later error.

Python – How should you cleanly restrict object property types and values in Python

Here is some code of mine without the TypeError: __call__() missing 1 required positional argument: 'self'. How do you create this error?

>>> class X(Exception):
    def __call__(self):
        raise self


>>> x = X()
>>> x()

Traceback (most recent call last):
  File "<pyshell#5>", line 1, in <module>
    x()
  File "<pyshell#3>", line 3, in __call__
    raise self
X
>>> class Other(X):
    pass

>>> o = Other()
>>> o()

Traceback (most recent call last):
  File "<pyshell#12>", line 1, in <module>
    o()
  File "<pyshell#3>", line 3, in __call__
    raise self
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