Randomly change the prompt in the Python interpreter

Question

It's kind of boring to always see the >>> prompt in Python. What would be the best way to go about randomly changing the prompt prefix?

I imagine an interaction like:

This is a tobbaconist!>> import sys
Sorry?>> import math
Sorry?>> print sys.ps1
Sorry?
What?>>

Just make sure you change it back before asking questions that include interpreter sessions... — jonrsharpe, Nov 12 '15 at 10:29
On the contrary, I think about making the questions stand out even more by using colors in the prompt (e.g. sys.ps1 = '\033[01;31mwhat?>>>\033[00m ') — mircealungu, Nov 12 '15 at 13:40
You could even have random colours to go with the tobacconist. — Holloway, Nov 12 '15 at 16:23
If you're changing the prompt colour and using readline, take a look at [this](https://stackoverflow.com/questions/9468435/look-how-to-fix-column-calculation-in-python-readline-if-use-color-prompt) question. — Holloway, Nov 12 '15 at 16:24
It might be a good idea to keep all of your random prompts a fixed width. Unless you like the extra challenge of counting your spaces and ignoring when things don't look lined up to make sure you indent properly. — tpg2114, Nov 12 '15 at 18:52

score 66 · Accepted Answer · answered Nov 12 '15 at 10:31

According to the docs, if you assign a non-string object to sys.ps1 then it will evaluate the str function of it each time:

If a non-string object is assigned to either variable, its str() is re-evaluated each time the interpreter prepares to read a new interactive command; this can be used to implement a dynamic prompt.

Well now it's obvious, you should make it dynamic! Make an object with a __str__ method where you can place any logic you want:

class Prompt:
    def __str__(self):
        # Logic to randomly determine string
        return string

You can also make changes or insert things into this class as you go too. So for example, you could have a list of messages in Prompt that you append to, or change, and that will affect the console message.

score 21 · Answer 2 · answered Nov 12 '15 at 10:31

21

Try this:

>>> import sys
>>> import random
>>> class RandomPrompt(object):
...     prompts = 'hello >', 'hi >', 'hey >'
...     def __repr__ (self): return random.choice(self.prompts)
... 
>>> sys.ps1 = RandomPrompt()
hello >1
1
hi >2
2

answered Nov 12 '15 at 10:31

Klaus D.

13,874
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`__repr__()` or `__str__()`? – glglgl Nov 12 '15 at 12:20
6

@glglgl, the prompt is generated by calling `__str__()`. If it's not defined, it defaults to `__repr__()` so in this case it doesn't matter which. – Holloway Nov 12 '15 at 12:38
Just to be sure: why would you want to write a class in this example. Wouldn't `def RandomPrompt(): prompts = [...]; return choice(prompts)` suffice? – andrepd Nov 12 '15 at 22:47
A function would run the initialization every time. In this particular case it wouldn't be expensive but it's generally a good practice to divide the initialization from the actual code. – Klaus D. Nov 13 '15 at 01:34

score 19 · Answer 3 · answered Nov 12 '15 at 10:23

For changing the prompt, we use

>>>import sys
>>>sys.ps1 = '=>'
=>

Now the way to do it randomly would be something like this:

import random
import sys

random_prompts = ['->', '-->', '=>', 'Hello->']
sys.ps1 = random.choice(random_prompts)

To execute this when your python interpreter starts, you can follow this guide: https://docs.python.org/2/tutorial/appendix.html#the-interactive-startup-file

score 8 · Answer 4 · answered Nov 12 '15 at 10:22

Nice question. The >>> prompt is in sys.ps1, the ... in sys.ps2. The next question would be how to change this randomly. Just as a demonstration of changing it by hand:

>>> import sys
>>> sys.ps1 = '<<<'
<<<sys.ps1 = '<<< '
<<< sys.ps2 = '.?. '
<<< for i in line:
.?.

Randomly change the prompt in the Python interpreter

4 Answers4