I want to keep a piece of code in a txt file and execute it from my Python script.
For example in the txt file there is
print("ok")
I want my programme to print ok and not print print("ok "). How can I do this?
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3You almost never want to do this but if you do, lookup exec. Horrible thing. shuddersmuddyfish– muddyfish2015-07-29 15:34:18 +00:00Commented Jul 29, 2015 at 15:34
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docs.python.org/2/library/functions.html#execfilexrisk– xrisk2015-07-29 15:38:56 +00:00Commented Jul 29, 2015 at 15:38
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Keep in mind that this is a grave security risk. Imagine what would happen if your file contained malicious code!xrisk– xrisk2015-07-29 15:39:27 +00:00Commented Jul 29, 2015 at 15:39
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I want to create a level editor for a game but this is the only way i think of, i need to stack data in an other file and then use itluka– luka2015-07-29 15:48:38 +00:00Commented Jul 29, 2015 at 15:48
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1I'd suggest you use some sort of structured text file for this. XML might be a good choice here. So you will store your game level information in xml file and use it in your game.konart– konart2015-07-29 15:51:42 +00:00Commented Jul 29, 2015 at 15:51
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3 Answers
Doing what you want usually is a security risk, but not necessarily so.
You'll definitely have to notify the user about potential risk.
There is more than one program using execfile() or compile() and exec statement to provide plug-ins system.
There is nothing so ugly about it, you just have to know what are you doing, when and where.
Both execfile(), eval() and exec statement allow you to specify a scope in which will your code be executed/evaluated.
myscope = {}
execfile("myfile.txt", myscope)
This will prevent the new code being mixed with the old one. All variables classes, functions and modules from myfile.txt will be contained in myscope dictionary.
This, however, does not prevent malicious code to delete all files it can from your disk or something similar.
Python 2 has a nice module called rexec, but from Python 2.2 it doesn't work any more.
It implements execfile() exec statement and eval() in restricted environment. Though it doesn't work it is there, and you can dig through the code to see how it is done.
So, you see, it is possible to allow only secure code to execute (well, as secure as it can be) from external source.
There is another way too. You can load the file, compile the code from it and then inspect it to see what it does. Then say, yes I'll execute it or no, I won't. This is, however, a little bit more work and a lot of complications.
But, I don't think that it'll be necessary to go through all that stuff. Please elaborate some more on your problem. What exactly do you mean by level editor? I don't think external code is a solution for that.
7 Comments
luka
Ok so my game is a spaceship that can shoot monsters basically so a level editor is for the user to simply create a level ( chose the type of monsters when it spawn chose the background etc ..) for exemple to create a monster its 5lines of code so when the user press new monster button it will automatically write those 5lines with his parameters in the txt file. That is my plan for now if you have an other idea please tell me
Dalen
You have a monster represented as an object I take it. If it is so then it is trivial to change it's attributes to reflect what you want. You can have more monster types defined and at the runtime do something like: 'newmonster = object(); newmonster.speed = 50; for x in dir(crocodile): setattr(newmonster, x, getattr(crocodile, x))'. In this way you will make new crocodile with speed 50. You can of course automatize it all by cleverly designed inheritance.
Dalen
To save it all, you can use configparser module to save only chosen attributes values as an INI file, or design some file of your own, or use pickle/cPickle module to save them as 'import cPickle as pickle; f = open("newmonster.txt", "wb"); pickle.dump(newmonster, f); f.close()' Loading will be done using pickle.load(), but to do it with dynamically filled objects will be a bit tricky. But it'll work.
luka
ok execfile fonction doesnt exist in python 3.0 and more you have to use exec(open("file.txt").read())
Dalen
Yes and no. It is possible to jam in more than one pickle in the file then parse it manually to separate them. Use pickle.dumps() and pickle.loads() instead of writing/loading directly to/from file. But it is easier to put all your objects into a dictionary or list and pickle it. Then when unpickling you just unpack that dict. It'll work flawlessly.
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You are looking for eval function
eval is a function that takes arbitrary python code represented as a string and execute it at run time.
Example
>>> x = 1
>>> y = eval('x+1')
>>> print(y)
2
It works in both Python 2.x and 3.x
Check the documentation : https://docs.python.org/2.7/library/functions.html#eval
2 Comments
Dalen
No it does not! eval() evaluates Python expressions, it doesn't execute arbitrary code. Try: 'eval("print 'abcd'")' and you'll get SyntaxError. :D But you're only half-wrong, as eval() allows execution of code objects and they may contain anything, not just expressions. So: 'eval(compile("print 'abcd'", "blah.py", "exec"))' will work.
Hamza Abbad
Thanks for the informations ! Next time I will test before answering
So I wanted to do the same thing. I came across this: GeeksforGeeks. With this we could make a text file. Let's say it's called myfile.txt and in the first line we will add print("ok") in the second add A += 1. Now let's move over to the script editor.
# open txt file
f = open("myfile.txt", "r")
# add the data in the file the a var
data = f.readlines()
# remove unwanted \n for new lines and '' left over by the code above
# readlines() returns a list so we need to convert data to str
# in data[] add the line you wish to read from
info = str(data[0]).strip("\n").strip("'")
# run the code
exec(info)
# running the A += 1 in the txt file
# run this
A = 0
info = str(data[1]).strip("\n").strip("'")
while A == 0:
print(A)
exec(info)
print(A)
# if you wanted too you can even define a variable with this
alist = ["B = 0", "B += 1", "print(B)"]
runner = [0, 1, 2, 1, 2, 0, 2]
for i in range(len(runner)):
exec(alist[int(runner[i])])
