Obtain function from string in python

Question

Is it possible to define a function to behave as follows?

text = "def x(a):\treturn a+1"
f = ??(text)
f(1)
>> 2

Why would you want to do this? If the reasoning is "because I want to define a function on the same line that I use it, and def can't be on the same line as other statements", then you can instead use lambdas: print (lambda a: a+1)(1) — Kevin
– Kevin, Commented Feb 25, 2015 at 13:32
@Kevin I am creating an API where the user can define functions that would be executed by other function (which are actually lambdas). — jamborta
– jamborta, Commented Feb 25, 2015 at 14:02

ForceBru · Accepted Answer · 2015-02-25 13:30:54Z

3

You can use exec()

text = "def x(a):\treturn a+1"
exec(text)
print x(5) # gives 6

answered Feb 25, 2015 at 13:30

ForceBru

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1 Comment

Kevin Over a year ago

Now the hard part is, getting f(5) to give 6, when you don't know the contents of text and don't know that the function is currently called x, and so you can't just do f = x

Hugh Bothwell · Accepted Answer · 2015-02-25 13:31:04Z

1

text = "lambda a: a + 1"
f = eval(text)
f(1)    # 2

answered Feb 25, 2015 at 13:31

Hugh Bothwell

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2 Comments

Hugh Bothwell Over a year ago

@bhargavrao: any method of running arbitrary code is dangerous.

Hugh Bothwell Over a year ago

@forcebru: yes, that's why I converted it to a lambda!

jamborta · Accepted Answer · 2015-03-02 17:28:11Z

0

here is another solution:

text = "def x(a):\treturn a+1"
f = {}
exec text in f
f['x'](1)
>> 2

answered Mar 2, 2015 at 17:28

jamborta

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1 Comment

CodeMouse92 Over a year ago

Please add some explanation. Imparting the underlying logic is more important than just giving the code, because it helps the OP and other readers fix this and similar issues themselves.

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