is there an 'execute' statement in python?

Question

Is there such a thing in python as an 'execute' statement that I can use similarly to the way I have below?

statement='print "hello world"'

def loop(statement):
    for i in range(100):
        for j in range(100):
            execute statement

loop(statement)

ThiefMaster · Answer 1 · 2012-05-27T22:23:58.083

10

Yes, simply pass a callable and use statement() to execute it.

A callable is a function, lambda expression or any other object that implements __call__.

def loop(func):
    for i in range(100):
        for j in range(100):
            func()

def say_hello():
    print "hello world"
loop(say_hello)

If you really want to execute code from a string (trust me, you don't!), there is exec:

>>> code = 'print "hello bad code"'
>>> exec code
hello bad code

edited May 27 '12 at 22:23

answered May 27 '12 at 21:52

ThiefMaster

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find another name for the statement function or it will be difficult for non-initiated pythonists to understand the difference with your callable argument in loop – Zeugma May 27 '12 at 21:58
Now it should be more obvious – ThiefMaster May 27 '12 at 21:59
functions *are* objects and they have `__call__` attribute. – jfs May 27 '12 at 22:22
why is it bad to execute code from a string? Using exec is a more brief way of doing it. – fergusdawson May 27 '12 at 22:55
1

@fergusdawson: it is much slower to execute, and if used in conjunction with user input can allow code injection attacks. – Hugh Bothwell May 27 '12 at 23:25
Is there any way in the example above that func() can access i and j in the enclosing function? When i try to reference the i in loop from func I get a global name not defined error. – fergusdawson May 27 '12 at 23:49
1

@fergusdawson, yes there is, but I'd encourage you to find a way to not need `exec` – John La Rooy May 28 '12 at 00:20
1

@fergusdawson: Why can't you pass them to the function as arguments? `func(i, j)` and `def say_hello(i, j): print 'hello world %d %d' % (i, j)` – ThiefMaster May 28 '12 at 00:29
@thiefmaster of course, that should have been obvious. thanks – fergusdawson May 28 '12 at 00:30
Great, if everything is solved please do not forget to accept the answer by clicking the gray checkmark icon on the left below the vote buttons. – ThiefMaster May 28 '12 at 00:54

is there an 'execute' statement in python?

1 Answers1