[Tutor] What exactly does the three dots do? Why such as thing?

[C W]

Today, I ran into ellipsis again. This time, it is COMPLETELY different
from before.

Here is a reproducible code:

import numpy as np
import matplotlib.pyplot as plt
...
x = np.linspace(0, 1)
y = np.sin(4 * np.pi * x) * np.exp(-5 * x)
plt.title('Week cycle')
plt.xlabel('Month')
plt.ylabel('Price')
plt.plot(x, y)


If I leave out the ellipsis, plot title and label will not show. It's doing
interactive plot. How am I suppose to know ellipsis is doing interactive
plotting? No way I could have guessed.

Matplotlib documentation <https://matplotlib.org/> explains that it
recreated itself from Matlab plots.

Is it something similar to Matlab like
>>> hold on;

That's fine! But, how many identities will ellipsis take on? How do you
experienced users deal with these ambiguities?



On Fri, Aug 11, 2017 at 9:24 PM, Steven D'Aprano <steve at pearwood.info>
wrote:

> On Fri, Aug 11, 2017 at 07:57:09AM -0600, Mats Wichmann wrote:
> > On 08/10/2017 05:23 PM, Alan Gauld via Tutor wrote:
> > > On 10/08/17 14:39, C W wrote:
> > >
> > >> I suppose it's just a place holder, though I don't know when I would
> use it
> > >> in my every day life.
> > >
> > > Probably never.
> > >
> > > Like most programming languages Python has a load of rarely used,
> > > obscure features. Most Python programmers never use ellipses,
> >
> > I guess what this means is when I post code snippets with some lines
> > elided for greater readability of the point being made I should not use
> > ellipses for that, as they're actually a syntactic element!   :)
>
> No, go right ahead and continue using ... for elided lines. Python 3
> makes that syntactically legal, and the fact that elided code may be
> syntactically correct is one of the reasons that was done.
>
> In Python 2, ... was just the *display* form of Ellipsis, and wasn't
> legal except in slice notation: a[...]. Python 3 made ... syntactic
> sugar for Ellipse everywhere, not just in slices, which makes:
>
>     x = ...
>
>     class X:
>         ...
>
> perfectly legal code. (Perhaps not *meaningful* code, but that's okay.)
>
>
> --
> Steve
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