# Python | Ellipse (different polygons) in Kiwi

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Kivy — it is a platform independent GUI tool in Python. Since it can run on Android, IOS, Linux, Windows, etc. It is mainly used to develop Android application, but that does not mean that it cannot be used in desktop applications.

## Ellipse:

Ellipse — this is the vertex canvas instruction. This allows you to draw a regular polygon or arc based on them. In this article, we will see that different polygons have a different number of sides, as well as many vertices on a circle.
As in Kivy, we can create polygons based on an ellipse. Note that angles in Kiwi are different from angles in mathematics. In Kiwi, the 0 degree point corresponds to the 90 degree point in mathematics.

Note:
These are the formulas for x and y. These math formulas assume the center is 0, 0. Thus, after calculations are done, there has to be a translation by x of a and y of b. The width is 2a, and height is 2b.

N segments = N vertices
1) angle [i] = i * 360 / n; i = 0 to n
2) x [i] = a cos (angle [i])
3) y [i] = b sin (angle [i])
4) In kivy 12’o clock is 0 degree and increases clockwise but in math 3’o clock is 0 degree increases counter clockwise.

A program to demonstrate how we can make different polygons in kiw with Ellipse.

main.py file:

 # Code for creating different polygons with Ellipse # import nodded module import kivy # this limits the kivy version ie # below this version you cannot # use an application or software Support kivy.require ( "1.9.1" ) # Your application base class inherits from the application class. # app: always refers to your application instance from kivy.app import App # GridLayout arranges children in a matrix. # It takes up available space and # divides it into columns and rows, # then adds widgets to the resulting "cells" . from kivy.uix.gridlayout import GridLayout # create a Layout class class Ellipsekv (GridLayout): pass # create application class class EllipseApp (App): def build ( self ): return Ellipsekv () # run application if __ name__ = = ’ __main__’ : EllipseApp (). run ()

Ellipse.kv file

 # Ellipse.kv code file ####### ########################################## # # For arcs, we have to give a start # and the ending angle. We use the default number of segments, # 180 and 5 for two elliptical arcs. # Rest part of the kv file matches another, # 6 elliptical arcs, following the same pattern. #: set angle_start_row2 240 #: set angle_end_row2 480 #: set angle_start_row3 120 #: set angle_end_row3 240 ########################### ###################### & lt; Ellipsekv & gt ;: # onki 4 cols: 4 ############### ################################### # Row 1 # Create canvas canvas: Color: rgb: 0 , 0 , 1 Rectangle: pos: self . pos size: self . size # This will create a circle # since no segment is captured in the ellipse # so it creates a circle by default RelativeLayout: canvas : Color: rgb: 1 ,. 8 ,. 5 Ellipse: pos: 0 , 0 size: self . size # This will create a pentagon like # segment = 5 RelativeLayout: canvas: Ellipse : segments: 5 pos: 0 , 0 size: self . size # This will create a square shape like # segment = 4 RelativeLayout: canvas: Ellipse: segments: 4 pos: 0 , 0 size: self . size # This will create a triangle like # segment = 3 RelativeLayout: canvas: Ellipse: segments: 3 pos: 0 , 0 size: self . size ###################### ########################### # Line 2 RelativeLayout: canvas: # Assign color to everyone on line 2 Color: rgb: 1 ,. 59 ,. 86 # Create an arc as above Ellipse: angle_start: angle_start_row2 angle_end: angle_end_row2 pos: 0 , 0 size : self . size # Create an arc as above # segment 5 RelativeLayout: canvas: Ellipse: angle_start: angle_start_row2 angle_end: angle_end_row2 segments: 5 pos: 0 , 0 size: self . size # Create an arc as above # segment 4 RelativeLayout: canvas: Ellipse: angle_start: angle_start_row2 angle_end: angle_end_row2 segments: 4 pos: 0 , 0 size: self . size # Create an arc as above # segment 5 RelativeLayout: canvas: Ellipse: angle_start: angle_start_row2 angle_end: angle_end_row2 segments: 3 pos: 0 , 0 size: self . size ####################### ########################## # row 3 RelativeLayout: canvas: Color: rgb:. 5 ,. 5 ,. 5 Ellipse: angle_start: angle_start_row3 angle_end: angle_end_row3 pos: 0 , 0 size: self . size RelativeLayout: canvas: Ellipse: angle_start: angle_start_row3 angle_end: angle_end_row3 segments: 5 pos: 0 , 0 size: self .size RelativeLayout: canvas: Ellipse: angle_start: angle_start_row3 angle_end: angle_end_row3 segments: 4 pos: 0 , 0 size: self . size RelativeLayout: canvas: Ellipse: angle_start: angle_start_row3 angle_end: angle_end_row3 segments: 3 pos: 0 , 0 size: self . size

Output:

This is the result. We have 3 rows and 4 columns. Rows 2 and 3 are arcuate, while row 1 has angles by default, 0 and 360, to form a full circle. By manually resizing the window, we can get ovals and shapes based on them. For an arc, the number of segments corresponds to the number of lines that approximate the circular part.

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## Python | Ellipse (different polygons) in Kiwi circle: Questions

How to do a scatter plot with empty circles in Python?

In Python, with Matplotlib, how can a scatter plot with empty circles be plotted? The goal is to draw empty circles around some of the colored disks already plotted by scatter(), so as to highlight them, ideally without having to redraw the colored circles.

I tried facecolors=None, to no avail.

204

From the documentation for scatter:

Optional kwargs control the Collection properties; in particular:

edgecolors:
The string ‚Äònone‚Äô to plot faces with no outlines
facecolors:
The string ‚Äònone‚Äô to plot unfilled outlines

Try the following:

import matplotlib.pyplot as plt
import numpy as np

x = np.random.randn(60)
y = np.random.randn(60)

plt.scatter(x, y, s=80, facecolors="none", edgecolors="r")
plt.show()

Note: For other types of plots see this post on the use of markeredgecolor and markerfacecolor.

## Python | Ellipse (different polygons) in Kiwi circle: Questions

plot a circle with pyplot

surprisingly I didn"t find a straight-forward description on how to draw a circle with matplotlib.pyplot (please no pylab) taking as input center (x,y) and radius r. I tried some variants of this:

import matplotlib.pyplot as plt
circle=plt.Circle((0,0),2)
# here must be something like circle.plot() or not?
plt.show()

... but still didn"t get it working.

199

You need to add it to an axes. A Circle is a subclass of an Patch, and an axes has an add_patch method. (You can also use add_artist but it"s not recommended.)

Here"s an example of doing this:

import matplotlib.pyplot as plt

circle1 = plt.Circle((0, 0), 0.2, color="r")
circle2 = plt.Circle((0.5, 0.5), 0.2, color="blue")
circle3 = plt.Circle((1, 1), 0.2, color="g", clip_on=False)

fig, ax = plt.subplots() # note we must use plt.subplots, not plt.subplot
# (or if you have an existing figure)
# fig = plt.gcf()
# ax = fig.gca()

fig.savefig("plotcircles.png")

This results in the following figure:

The first circle is at the origin, but by default clip_on is True, so the circle is clipped when ever it extends beyond the axes. The third (green) circle shows what happens when you don"t clip the Artist. It extends beyond the axes (but not beyond the figure, ie the figure size is not automatically adjusted to plot all of your artists).

The units for x, y and radius correspond to data units by default. In this case, I didn"t plot anything on my axes (fig.gca() returns the current axes), and since the limits have never been set, they defaults to an x and y range from 0 to 1.

Here"s a continuation of the example, showing how units matter:

circle1 = plt.Circle((0, 0), 2, color="r")
# now make a circle with no fill, which is good for hi-lighting key results
circle2 = plt.Circle((5, 5), 0.5, color="b", fill=False)
circle3 = plt.Circle((10, 10), 2, color="g", clip_on=False)

ax = plt.gca()
ax.cla() # clear things for fresh plot

# change default range so that new circles will work
ax.set_xlim((0, 10))
ax.set_ylim((0, 10))
# some data
ax.plot(range(11), "o", color="black")
# key data point that we are encircling
ax.plot((5), (5), "o", color="y")

fig.savefig("plotcircles2.png")

which results in:

You can see how I set the fill of the 2nd circle to False, which is useful for encircling key results (like my yellow data point).

How do I install pip on macOS or OS X?

I spent most of the day yesterday searching for a clear answer for installing pip (package manager for Python). I can"t find a good solution.

How do I install it?

1672

UPDATE (Jan 2019):

easy_install pip

If you need admin privileges to run this, try:

sudo easy_install pip

1672

‚ö°Ô∏è TL;DR ‚Äî One line solution.

All you have to do is:

sudo easy_install pip

2019: ‚ö†Ô∏èeasy_install has been deprecated. Check Method #2 below for preferred installation!

Details:

‚ö°Ô∏è OK, I read the solutions given above, but here"s an EASY solution to install pip.

MacOS comes with Python installed. But to make sure that you have Python installed open the terminal and run the following command.

python --version

If this command returns a version number that means Python exists. Which also means that you already have access to easy_install considering you are using macOS/OSX.

‚ÑπÔ∏è Now, all you have to do is run the following command.

sudo easy_install pip

After that, pip will be installed and you"ll be able to use it for installing other packages.

Let me know if you have any problems installing pip this way.

Cheers!

P.S. I ended up blogging a post about it. QuickTip: How Do I Install pip on macOS or OS X?

‚úÖ UPDATE (Jan 2019): METHOD #2: Two line solution ‚Äî

curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py

Now run this file to install pip

python get-pip.py

That should do it.

Another gif you said? Here ya go!

1672

You can install it through Homebrew on OS X. Why would you install Python with Homebrew?

The version of Python that ships with OS X is great for learning but it‚Äôs not good for development. The version shipped with OS X may be out of date from the official current Python release, which is considered the stable production version. (source)

Homebrew is something of a package manager for OS X. Find more details on the Homebrew page. Once Homebrew is installed, run the following to install the latest Python, Pip & Setuptools:

brew install python

We hope this article has helped you to resolve the problem. Apart from Python | Ellipse (different polygons) in Kiwi, check other circle-related topics.

Want to excel in Python? See our review of the best Python online courses 2022. If you are interested in Data Science, check also how to learn programming in R.

By the way, this material is also available in other languages:

Xu Galleotti

Singapore | 2022-12-10

circle is always a bit confusing 😭 Python | Ellipse (different polygons) in Kiwi is not the only problem I encountered. I am just not quite sure it is the best method

Anna Galleotti

Prague | 2022-12-10

Thanks for explaining! I was stuck with Python | Ellipse (different polygons) in Kiwi for some hours, finally got it done 🤗. Will get back tomorrow with feedback

Boris Galleotti

Paris | 2022-12-10

Thanks for explaining! I was stuck with Python | Ellipse (different polygons) in Kiwi for some hours, finally got it done 🤗. I just hope that will not emerge anymore

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