Quick-and-dirty IPC with Python, JSON and pyperclip

By Vasudev Ram

Blue Gene image attribution

Hi, readers,

Some time ago I had written this post.

pyperclip, a cool Python clipboard module


The pyperclip module allows you to programmatically copy/paste text to/from the system clipboard.

Recently, I realized that pyperclip's copy and paste functionality could be used to create a sort of rudimentary IPC (Inter Process Communication) between two Python programs running on the same machine.

So I whipped up a couple of small programs, a sender and a receiver, as a proof of concept of this idea.

Here is the sender, pyperclip_ipc_sender.py:

'''
pyperclip_ipc_sender.py
Purpose: To send JSON data to the clipboard from  
a Python object.
Author: Vasudev Ram
Copyright 2018 Vasudev Ram
Web site: https://vasudevram.github.io
Blog: https://jugad2.blogspot.com
Training: https://jugad2.blogspot.com/p/training.html
Product store: https://gumroad.com/vasudevram
'''

from __future__ import print_function
import pyperclip as ppc
import json
import pprint

def generate_data():
    d = {"North": 1000, "South": 2000, "East": 3000, "West": 4000}
    return d

def send_data(d):
    ppc.copy(json.dumps(d))

def main():
    print("In pyperclip_ipc_sender.py")
    print("Generating data")
    d = generate_data()
    print("data is:")
    pprint.pprint(d)
    print("Copying data to clipboard as JSON")
    send_data(d)

main()

And here is the receiver, pyperclip_ipc_receiver.py:

'''
pyperclip_ipc_receiver.py
Purpose: To receive JSON data from the clipboard into 
a Python object and print it.
Author: Vasudev Ram
Copyright 2018 Vasudev Ram
Web site: https://vasudevram.github.io
Blog: https://jugad2.blogspot.com
Training: https://jugad2.blogspot.com/p/training.html
Product store: https://gumroad.com/vasudevram
'''

from __future__ import print_function
import pyperclip as ppc
import json
import pprint

def receive_data():
    d = json.loads(ppc.paste())
    return d

def main():
    print("In pyperclip_ipc_receiver.py")
    print("Pasting data from clipboard to Python object")
    data = receive_data()
    print("data is:")
    pprint.pprint(data)

main()

First I ran the sender in one command window:

$ python pyperclip_ipc_sender.py
In pyperclip_ipc_sender.py
data is:
{'East': 3000, 'North': 1000, 'South': 2000, 'West': 4000}
Copying data to clipboard as JSON

Then I ran the receiver in another command window:

$ python pyperclip_ipc_receiver.py
In pyperclip_rpc_receiver.py
Pasting data from clipboard to Python object
data is:
{u'East': 3000, u'North': 1000, u'South': 2000, u'West': 4000}

You can see that the receiver has received the same data that was sent by the sender - via the clipboard.

A few points about this technique:

- If you run the receiver without running the sender, or even before running the sender, the receiver will pick up whatever data was last put into the clipboard, either by some other program, or manually by you. For example, if you selected some text in an editor and then pressed Ctrl-C (to copy the selected text to the clipboard), the receiver would get that text (if it was JSON text - see two points below). However, that is not a bug, but a feature :)

- Obviously, this is not meant for production use, due to potential security issues. It's just a toy application as a proof of concept of this idea.

- Since I convert the Python object data to JSON in the sender before copying it to the clipboard with pyperclip, the receiver also expects the data it pastes from the clipboard into a Python object to be of type JSON. So if you instead copy some non-JSON data to the clipboard and then run the receiver, you will get an error. I tried this, and got:

ValueError: No JSON object could be decoded

To handle this gracefully, you can trap the ValueError (and maybe other kinds of exceptions that Python's json library may raise), with a try-except block around the code that pastes the data from the clipboard. You can then either tell the user to try again, or print/log the error and exit, depending on whether the receiver was an interactive or a non-interactive program.

The image at the top of the post is of an IBM Blue Gene supercomputer.

From the Wikipedia article about it:

[ The project created three generations of supercomputers, Blue Gene/L, Blue Gene/P, and Blue Gene/Q. Blue Gene systems have often led the TOP500[1] and Green500[2] rankings of the most powerful and most power efficient supercomputers, respectively. Blue Gene systems have also consistently scored top positions in the Graph500 list.[3] The project was awarded the 2009 National Medal of Technology and Innovation.[4] ]

- Enjoy.

---

- Vasudev Ram - Online Python training and consulting

---

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---

pyperclip, a cool Python clipboard module

By Vasudev Ram

I recently came across this neat Python library, pyperclip, while browsing the net. It provides programmatic copy-and-paste functionality. It's by Al Sweigart.

pyperclip is very easy to use.

I whipped up a couple of simple programs to try it out.

Here's the first one, pyperclip_json_test.py:

from __future__ import print_function
import pyperclip as ppc
import json

d1 = {}
keys = ("TS", "TB")
vals = [
    ["Tom Sawyer", "USA", "North America"],
    ["Tom Brown", "England", "Europe"],
]
for k, v in zip(keys, vals):
    d1[k] = v
print("d1:")
for k in keys:
    print("{}: {}".format(k, d1[k]))

ppc.copy(json.dumps(d1))
print("Data of dict d1 copied as JSON to clipboard.")
d2 = json.loads(ppc.paste())
print("Data from clipboard copied as Python object to dict d2.")
print("d1 == d2:", d1 == d2)

The program creates a dict, d1, with some values, converts it to JSON and copies that JSON data to the clipboard using pyperclip.
Then it pastes the clipboard data into a Python string and converts that to a Python dict, d2.

Here's a run of the program:

$ python pyperclip_json_test.py
d1:
TS: ['Tom Sawyer', 'USA', 'North America']
TB: ['Tom Brown', 'England', 'Europe']
Data of dict d1 copied as JSON to clipboard.
Data from clipboard copied as Python object to dict d2.
d1 == d2: True

Comparing d1 and d2 shows they are equal, which means the copy from Python program to clipboard and paste back to Python program worked okay.

Here's the next program, pyperclip_text_stats.py:

from __future__ import print_function
import pyperclip as ppc

text = ppc.paste()
words = text.split()
print("Text copied from clipboard:")
print(text)
print("Stats for text:")
print("Words:", len(words), "Lines:", text.count("\n"))

"""
the quick brown fox 
jumped over the lazy dog
and then it flew over the rising moon
"""

The program pastes the current clipboard content into a string, then finds and prints the number of words and lines in that string. No copy in this case, just a paste, so your clipboard should already have some text in it.

Here are two runs of the program. Notice the three lines of text in a triple-quoted comment at the end of the program above. That's my test data. For the first run below, I selected the first two lines of that comment in my editor (gvim on Windows) and copied them to the clipboard with Ctrl-C. Then I ran the program. For the second run, I copied all the three lines and did Ctrl-C again. You can see from the results that it worked; it counted the number of lines and words that it pasted from the clipboard text, each time.

$ python pyperclip_text_stats.py
Text copied from clipboard:
the quick brown fox
jumped over the lazy dog

Stats for text:
Words: 9 Lines: 2

$ python pyperclip_text_stats.py
Text copied from clipboard:
the quick brown fox
jumped over the lazy dog
and then it flew over the rising moon

Stats for text:
Words: 17 Lines: 3

So we can see that pyperclip, as used in this second program, can be useful to do a quick word and line count of any text you are working on, such as a blog post or article. You just need that text to be in the clipboard, which can be arranged just by selecting your text in whatever app, and doing a Ctrl-C. Then you run the above program. Of course, this technique will be limited by the capacity of the clipboard, so may not work for large text files. That limit could be found out by trial and error, e.g. by copying successively larger chunks of text to the clipboard, pasting them back somewhere else, comparing the two, and checking whether or not the whole text was preserved across the copy-paste. There could be a workaround, and I thought of a partial solution. It would involve accumulating the stats for each paste, into variables, e.g. total_words += words and total_lines += lines. The user would need to keep copying successive chunks of text to the clipobard. How to sync the two, user and this modified program? Need to think it through, and it might be a bit clunky. Anyway, this was just a proof of concept.

As the pyperclip docs say, it only supports plain text from the clipboard, not rich text or other kinds of data. But even with that limitation, it is a useful library.

The image at the top of the post is a partial screenshot of my vim editor session, showing the menu icons for cut, copy and paste.

You can read about the history and evolution of cut, copy and paste here:

Cut, copy, and paste

New to vi/vim and want to learn its basics fast? Check out my vi quickstart tutorial. I first wrote it for a couple of Windows sysadmin friends of mine, who needed to learn vi to administer Unix systems they were given charge of. They said the tutorial helped them to quickly grasp the basics of text editing with vi.

Of course, vi/vim is present, or just a download away, on many other operating systems by now, including Windows, Linux, MacOS and many others. In fact, it is pretty ubiquitous, which is why vi is a good skill to have - you can edit text files on almost any machine with it.

- Enjoy.

---

- Vasudev Ram - Online Python training and consulting

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