Embedding executable python script in python string

Question

If you are a bash/posix sh wizard you will know the $(command substition) feature in bash, which could even be inserted in a string. For example,

$ echo "I can count: $(seq 1 10 | tr -d '\n')" 
I can count: 12345678910

You can imagine all wild things to do with this, especially to make a dynamically formed string. No need to do if..else block outside the string; just embed the code inside! I am s spoiled by this feature. So here's the question: in python, can we do something similar? Is there one person already devising a module to accomplish this task?

(Just a side comment: admittedly having this kind of feature is powerful but also opening yourself to a security risk. The program can be vulnerable to code injection. So think thoroughly before doing this especially with a foreign string coming from outside the code.)

I don't see how print "I can count: $(''.join(map(str,range(1,11))))" is any better than, for example, print "I can count: %s" % ''.join(map(str,range(1,11))) — Jimmy
– Jimmy, Commented Sep 9, 2011 at 16:48
Yeah, you can do this kind of thing in Python without eval and friends. @Jimmy nothing wrong with your answer, or join(str(x) for x in range(1, 11)) — agf
– agf, Commented Sep 9, 2011 at 17:32
Just for clarity: I don't intend to reproduce that same exact action (in the snippet) in python. Not at all. I am making an input file for a scientific code and usually some parameters (say, nexpand) can depend on another parameter (say, size) in a fancy way. — Wirawan Purwanto
– Wirawan Purwanto, Commented Sep 9, 2011 at 17:39

Community · Accepted Answer · 2017-05-23 10:24:35Z

1

You can use eval() and all of it's potential risks...

Some good links here and here

edited May 23, 2017 at 10:24

CommunityBot

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answered Sep 9, 2011 at 16:44

hymloth

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1 Comment

Wirawan Purwanto Over a year ago

Thanks for the pointer. They are very interesting (I keep them in my clipping)! But in my question I am not concerned with security issues at all, since these are all private scripts and won't be run in a server at large. The strings to be executed will be my string, not a foreign string. I am just attaching the parenthetical comment so other people would not blindly use this technique without knowing what they are getting into.

Alex Smith · Accepted Answer · 2011-09-09 16:45:00Z

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See the built-in eval() function.

answered Sep 9, 2011 at 16:45

Alex Smith

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Shaurya Chhabra · Accepted Answer · 2022-01-30 05:57:41Z

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Are you looking for an fstring: Instead of starting the string with ' We start the string with f' And whenever we want to embed any script we just put inside these: {}

answered Jan 30, 2022 at 5:57

Shaurya Chhabra

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