On 26/11/2017 09:09, Greg Tibbet wrote:
I'm an old timer, have programmed in Fortran, C, C++, Perl, and a bit
of Java and trying to learn this new-fangled Python language!
I've got a small program that uses PIL to create an image, draw some
primitives (rectanges, ellipses, etc...) and save it. Works fine...
no issues.
I've found in the past, the best way to "really learn" the language
was to "dig into the guts" and understand it,.. I thought I was making
progress, but when looking into the PIL library to see what's going on
behind the scenes, I find the following code in ImageDraw.py
def ellipse(self, xy, fill=None, outline=None):
"""Draw an ellipse."""
ink, fill = self._getink(outline, fill)
if fill is not None:
self.draw.draw_ellipse(xy, fill, 1)
<...snipped...>
ellipse() uses the method self.draw.draw_ellipse() Okay, fine...
but WHERE is draw_ellipse defined?? What magic is happening there?
I've searched the entire PIL directory tree, and the ONLY two places
draw_ellipse is mentioned are right there in the ellipse() function...
WHAT am I missing??
Python isn't a very pure language in that much of the functionality that
looks like it should be written in Python (because you imported a module
just like you import any Python module), actually is written in
something else, as has been pointed out.
It's reasonable that some things need to be implemented using some
foreign functions. But the boundary between Python and non-Python is
blurred.
Take this program:
import sys
and try and find sys.py in your installation.
(This is an obstacle if, for example, you're thinking of implementing a
Python interpreter. In theory, once you have it working, it should run
any .py program. But the critical modules it needs don't have .py source
code. And the interface to those non-Python functions isn't defined with
special byte-code instructions.
(It will be done /via/ those instructions, but the magic needed is on
the other side of them. Calling into sys.fn() uses the same
CALL_FUNCTION byte-code as calling into a regular Python function.)
As I said, it's not pure. More of a jungle as you've found out.)
--
bartc
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