python-fun | Some fun and useful projects with Python

As mentioned in the comments, in the first iteration of the for-loop, "i" is 0. You should take into account that the calculated value may become negative (hence the ValueError: sleep length must be non-negative).

You can use max(0, start_time + i*interval - time.time()) or change the range to range(1,21) to prevent this from happening.

As far as the differences between Pycharm and on the Raspberry, it might have to do with the clock precision of the two machines (different time yield by time.time())

You are giving the value $ts_name to python as string, bash does not do anything with it. You need to close the ', so that it becomes a string in bash, and then open it again for it to become a string in python.

The result will be something like this:

Thank you to @arturaz for explaining the Basic array comes to python as a tuple and needs converting to a list (best match for an array in python). Further details are given in his answer at https://stackoverflow.com/a/8978435/4539999 which builds on the question and other answer.

The APSO python console shows:

1. what is parsed from Basic to python
2. what is required
3. required data with dates formatted

Figured it out. These work

assertRaises takes a callable as its (optional) second argument. Since .get(...) is not a callable, you should use the context manager form instead:

You can use forward references:

The code you use is a brief description of the exclusive use within a directly defined template.
To use a custom function within a template used by render_template, you have to add it to the dictionary globals of the jinja environment.

Your conversion function simply needs to create a new function that calls the original function with self._obj as the first argument.

I got curious if I write len(nums) in while will my program do more computations.

One aspect of this is documented in the Python wiki's TimeComplexity page for all built-in data structures. len() for a list is O(1).

If you mean something along the lines of

will my program be faster if I do n = len(nums), then manually subtract 1 from n each time I remove from the list

then that's a whole other question, and the answer is likely (measure it!) to be (perhaps somewhat unintuitively) "no", since len() is implemented in C (fast!) and interpreting Python code (n -= 1) and executing it is slower.

How to look for the source code of builtin functions without manually searching the source code on GitHub?

As prerequisites, you will need to

• know how to read C and understand the control flow
• be able to keep track of the call graph (in your head, in a text file, on a notepad)
• have an intuition of where you start looking in the source code

GitHub's source code search is, well, passable, but you'll have a better time downloading the source and using a better IDE to jump around in the code.

For built-in functions in modules, I'd start searching for e.g. mathmodule.c for the math functions, etc.

For implementations of objects, there's e.g. listobject.c. It's fairly logical (most of the time).

1. You already found builtin_len.
2. You can see it calls PyObject_Size. That's defined here.
3. It does PySequenceMethods *m = Py_TYPE(o)->tp_as_sequence;, i.e. grabs a pointer to the type header of the object, and the "slot" (not to be confused with the Python userland slots) of the sequence-related methods for the object.
4. If that method collection contains a valid sq_length() function, it is called: Py_ssize_t len = m->sq_length(o); If that length is valid, it is returned, and len() wraps the bare size_t into a Python long object and passes it to you.
5. If that fails, PyMapping_Size gets called.
6. It does a similar thing as the sq_length stuff, only using mapping methods, tp_as_mapping and mp_length.
7. If all that fails, a TypeError is raised using the type_error() helper.

Here in listobject.c, you can see how list_length() is hooked up to be sq_length for list objects.

That function only calls Py_SIZE()[https://docs.python.org/3/c-api/structures.html#c.Py_SIZE], which is a macro to access the ob_size field which all PyVarObjects have.

The documentation on find how Python's list objects use ob_size is here.

As for how a custom type with __len__ hooks up into all of this, my recollection is that objects with __len__ will have their sq_length() call the Python callable, if one exists, and that value is then "trampolined" back through the C code back to your Python code.