Latest Python recipes

Shoelace Formula for polygonal area (Python)

2017-07-17T05:53:45-07:00

Python recipe 580812 by Paddy McCarthy (2d, area).

Copied, by author from "Paddy3118 Go deh!: Python investigation of the Shoelace Formula for polygonal area http://paddy3118.blogspot.com/2017/07/python-investigation-of-shoelace.html#ixzz4n43Dqhaa " Where there is more meat on the bone (under a different license though).

Uno (Text-Based) (Python)

2017-07-15T00:46:59-07:00

Python recipe 580811 by Brandon Martin (artificial_intelligence, cards, game, text_game, uno).

A text based recreation of the classic card game featuring functional AIs to play with. Some rules have been modified. User interface is text based, non-curses, using only simple python commands to draw it.

How to create a simple PDF Pie Chart using fitz / PyMuPDF (Python)

2017-07-10T16:07:51-07:00

Python recipe 580810 by Jorj X. McKie (fitz, pdf_generation).

PyMuPDF now supports drawing pie charts on a PDF page.

Important parameters for the function are center of the circle, one of the two arc's end points and the angle of the circular sector. The function will draw the pie piece (in a variety of options) and return the arc's calculated other end point for any subsequent processing.

This example creates a chart of the parliament seat distribution for political parties in the current German Bundestag.

Insert a Text Box in a PDF page (fitz / PyMuPDF) (Python)

2017-06-29T22:54:25-07:00

Python recipe 580809 by Jorj X. McKie (fitz, mupdf, pdf, textbox).

This method inserts text into a predefined rectangular area of a (new or existing) PDF page. Words are distributed across the available space, put on new lines when required etc. Line breaks and tab characters are respected / resolved. Text can be aligned in the box (left, center, right) and fonts can be freely chosen. The method returns a float indicating how vertical space is left over after filling the area.

Guard against an exception in the wrong place (Python)

2017-06-25T17:17:43-07:00

Python recipe 580808 by Steven D'Aprano (context, exception, guard, manager). Revision 2.

Sometimes exception handling can obscure bugs unless you guard against a particular exception occurring in a certain place. One example is that accidentally raising StopIteration inside a generator will halt the generator instead of displaying a traceback. That was solved by PEP 479, which automatically has such StopIteration exceptions change to RuntimeError. See the discussion below for further examples.

Here is a class which can be used as either a decorator or context manager for guarding against the given exceptions. It takes an exception (or a tuple of exceptions) as argument, and if the wrapped code raises that exception, it is re-raised as another exception type (by default RuntimeError).

For example:

try:
    with exception_guard(ZeroDivisionError):
        1/0  # raises ZeroDivisionError
except RuntimeError:
    print ('ZeroDivisionError replaced by RuntimeError')


@exception_guard(KeyError)
def demo():
    return {}['key']  # raises KeyError

try:
    demo()
except RuntimeError:
    print ('KeyError replaced by RuntimeError')

Variable Abbreviations (Python)

2017-06-22T11:57:20-07:00

Python recipe 580807 by Alfe (abbreviations, contextmanager, variables, with).

One sometimes has nice long speaking names vor variables, maybe things like buildingList[foundIndex].height, but would like to address these in a shorter fashion to be used within a formula or similar where lots of longs names tend to confuse any reader trying to understand the formula. Physicists use one-letter names for a reason.

For this I wrote a small context provider which allows using short names instead of long ones:

with Abbr(h=buildingList[foundIndex].height, g=gravitationalConstant):
    fallTime = sqrt(2 * h / g)
    endSpeed = sqrt(2 * h * g)
print("Fall time:", fallTime)
print("End speed:", endSpeed)

For longer formulas this can reduce ugly multi-line expressions to clearly readable one-liners.

One could use this:

h = buildingList[foundIndex].height
g = gravitationalConstant
fallTime = sqrt(2 * h / g)
endSpeed = sqrt(2 * h * g)
del g, h
print("Fall time:", fallTime)
print("End speed:", endSpeed)

to achieve the same result, but

it would not look as clean and
the context provider solves the typical issues like cleanup on exception etc.

Just using local variables without cleanup (like above without the del statement) also is an option of course, but that would clutter the variable name space unnecessarily.

CAVEATS: The implementation of Abbr() is a hack. If used as intended and described here, it should work just fine, though. But the hackish nature forces me to mention some things: Since at compile time the compiler decides that the h and g in the example must be global variables (because they aren't assigned in the function), it produces byte code accessing global variables. The context provider changes the global variable structure to fill the needs. (Overridden already existing global variables of the same name get restored properly at context exit.) This means some things:

One cannot have a local variable of the same name in the frame surrounding the context manager.
Existing global variables are changed during the time of the context manager; so using names like sys or os for abbreviations might be a bad idea due to side-effects.

How to Create a PDF with a Caustic Drawing (Python)

2017-06-18T17:43:47-07:00

Python recipe 580806 by Jorj X. McKie (fitz, mupdf, pdf, pymupdf).

Just a little demo on how to create simple drawings with PyMuPDF.

This script simulates what you see looking into your coffee mug, early in the morning after a long night of programming ...

Create Calendars on PDF with a few lines (Python)

2017-06-13T10:57:34-07:00

Python recipe 580805 by Jorj X. McKie (calendar, fitz, mupdf, pdf, pymupdf). Revision 2.

PyMuPDF (fitz) provides easy to use ways to create PDF documents out of simple texts.

An example is the text output of Python's calendar module. Here we take a starting year as script parameter and output a 3-page (A4 landscape) document with calendars for this and the following two years - in less than 20 lines of code.

Inserting Images on PDF Pages (Python)

2017-05-17T21:10:26-07:00

Python recipe 580803 by Jorj X. McKie (fitz, mupdf, pdf, pymupdf).

Version 1.11.0 of PyMuPDF allows putting an image on an existing PDF page. The following example puts the same image on every page of a given PDF - like a thumbnail.

Inserting pages into a PDF with PyMuPDF (Python)

2017-05-17T21:15:26-07:00

Python recipe 580802 by Jorj X. McKie (fitz, mupdf, pdf, text_conversion). Revision 2.

Version 1.11.0 of PyMuPDF allows creating new PDF pages, as well as inserting images into existing pages.

Here is a script that converts any textfile into a PDF.

groupby() For Unsorted Input (Python)

2017-05-12T10:40:58-07:00

Python recipe 580800 by Alfe (algorithm, datastructures, generators, grouping, lazy).

We all know the groupby() which is available in the itertools standard module. This one yields groups of consecutive elements in the input which are meant to be together in one group. For non-consecutive elements this will yield more than one group for the same key.

So effectively, groupby() only reformats a flat list into bunches of elements from that list without reordering anything. In practice this means that for input sorted by key this works perfect, but for unsorted input it might yield several groups for the same key (with groups for other keys in between). Typically needed, though, is a grouping with reordering if necessary.

I implemented a likewise lazy function (yielding generators) which also accepts ungrouped input.

Tkinter frame with different border sizes (Python)

2017-05-06T18:45:00-07:00

Python recipe 580798 by Miguel Martínez López (border, size, tkinter).

This trick shows how to create a bordered frame with different border size in each side.

Scrolled Frame V2 (Python)

2017-05-06T18:54:47-07:00

Python recipe 580797 by Miguel Martínez López (frame, scrolling, tkinter). Revision 4.

This is another version of scrolled frame. It doesn't use Canvas. Instead it does the trick using place geometry manager.

Based on these codes:

https://github.com/alejandroautalan/pygubu/blob/master/pygubu/widgets/tkscrolledframe.py
http://wiki.tcl.tk/9223

This is my other version of scrolled frame:

https://code.activestate.com/recipes/580640-scrolling-frame-with-mouse-wheel-support/

How to handle PDF embedded files with PyMuPDF (Python)

2017-07-11T18:57:54-07:00

Python recipe 580796 by Jorj X. McKie (embedded_files, fitz, mupdf, pdf, pymupdf). Revision 3.

Version 1.11.0 (based on MuPDF v1.11) allows exporting, importing and interrogating files embedded in a PDF.

PDF "/EmbeddedFiles" are similar to ZIP archives (or the Microsoft OLE technique), allowing arbitrary data to be incorporated in a PDF and benefit from its unique features.

bind all tkinter "bug" (Python)

2017-05-05T20:33:31-07:00

Python recipe 580795 by Miguel Martínez López (all, bind, binding, tkinter). Revision 3.

This recipes tries to solve the problem of bind_all and unbind_all for tkinter.

When a callback is registered using bind_all method and later it's unregistered using unbind_all, all the callbacks are deleted for the "all" tag event. This makes difficult to register and unregister only one callback at a time. This recipes tries to solve this problem.

Observe the difference between the code below and the recipe. With the code below, when the user clicks nothing happens. But with my recipe it's possible to bind and unbind specific callbacks.

try:
    from Tkinter import Tk, Frame
except ImportError:
    from tkinter import Tk, Frame

root = Tk()
f = Frame(root, width= 300, height=300)
f.pack()

def callback1(event):
    print("callback1")

def callback2(event):
    print("callback2")

def callback3(event):
    print("callback3")

root.bind_all("<1>", callback1, add="+")
f.bind_all("<1>", callback2, add="+")
f.bind_all("<1>", callback3, add="+")

f.unbind_all("<1>")

root.mainloop()

Simple multicolumn listbox for tkinter (Python)

2017-05-02T22:27:15-07:00

Python recipe 580794 by Miguel Martínez López (listbox, multicolumn, table, tkinter).

This recipe makes easy to work a treeview widget like a table.

It has several options for styling:

heading_anchor
heading_font
heading_background
heading_foreground
cell_anchor
cell_background
cell_foreground
cell_font
cell_pady
height
padding
adjust_heading_to_content
stripped_rows
headers
selection_background
selection_foreground
field_background

The "command" parameter is a callback and its called each time a row is selected.

Tkinter table with scrollbars (Python)

2017-05-06T19:06:05-07:00

Python recipe 580793 by Miguel Martínez López (scrollbars, table, tkinter). Revision 13.

I created here a tkinter table with scrollbar support. I use one of my other recipes for the mousewheel support and scrolling:

https://code.activestate.com/recipes/580640-scrolling-frame-with-mouse-wheel-support

Classifying characters using nested conditional expressions (Python)

2017-04-27T21:26:00-07:00

Python recipe 580792 by Vasudev Ram (characters, classification, conditional_expressions, expressions, join, lambda, map).

Python has a feature called conditional expressions, similar to C's ternary operator. For example:

print n, 'is odd' if n % 2 == 1 else 'is even'

Here, the conditional expression is this part of the print statement above:

'is odd' if n % 2 == 1 else 'is even'

This expression evaluates to 'is odd' if the condition after the if keyword is True, and evaluates to 'is even' otherwise.

The Python Language Reference section for conditional expressions shows that they can be nested. This recipe shows that we can use nested conditional expressions (within a return statement in a user-defined function) to classify characters into lowercase letters, uppercase letters, or neither.

It also shows how to do the same task using map, lambda and string.join, again with a nested conditional expression, but without using return or a user-defined function.

Auto assign self attributes in init using PEP 484 (Python)

2017-04-26T17:26:29-07:00

Python recipe 580790 by Ryan Gonzalez (annotations, class, self, type). Revision 2.

TL;DR: Short way of doing stuff like def __init__(self, a, b): self.a = a; self.b = b, using type annotations from PEP 484, inspired by Dart's MyConstructor(this.a, this.b) and Ruby's/Crystal's/(Moon|Coffee)Script's constructor/initialize(@a, @b).

Implementing class-based callbacks in Python (Python)

2017-04-20T23:34:50-07:00

Python recipe 580788 by Vasudev Ram (callbacks, classes, functions, methods, objects, programming, python).

This is a follow-on to this recently posted recipe:

Implementing function-based callbacks in Python: https://code.activestate.com/recipes/580787-implementing-function-based-callbacks-in-python/?in=user-4173351

This new recipe shows how to create and use callbacks in Python, using classes with methods, instead of plain functions, as was done in the recipe linked above. All other points such as reasons and benefits for using callbacks, are more or less the same as mentioned in the previous recipe, except that class instances can carry state around, so to that extent, the two approaches are different.

https://jugad2.blogspot.in/2017/04/python-callbacks-using-classes-and.html