Lazy list of functions

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April 15th, 2008, 03:48 AM

aamay

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Lazy list of functions

Hi folks,

I'm trying to write a test script without dozens of ifs. I was hoping to put all my tests into a list of functions and then do something like a left fold over it and add embelishments for printing the name of the test and its result. Trouble is, I can't seem to create that list of functions because python just evaluates them straight away and puts the results in the list instead. This seems to belie the statement that functions are first class objects. Is there something like lisp's tick to solve this, or should I resort to comefrom?

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April 15th, 2008, 07:09 AM

SuperOscar

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The following has probably serious consequences or side effects, but I leave that to more knowledgeable persons.

How about having a list of strings where each string is the name of a function, and then eval()ling each name?

Python Code:

Original - Python Code
def test1: print 'Running test 1...' # ...and so on funcs = ['test1', 'test2', 'test3'] for func in funcs: eval('%s()' % func)

def test1:
    print 'Running test 1...'
# ...and so on
funcs = ['test1', 'test2', 'test3']
for func in funcs:
    eval('%s()' % func)

April 15th, 2008, 08:34 AM

bvdet

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The following utilizes a tuple of functions. Functions are first-class objects in Python.

Python Code:

Original - Python Code
def fdim(s): ss = s.split('/') return float(ss[0])/float(ss[1]) def convertType(s): if s != 'None': for func in (int, float, fdim, eval): try: n = func(s) return n except: pass return s

def fdim(s):
    ss = s.split('/')
    return float(ss[0])/float(ss[1])
 
def convertType(s):
    if s != 'None':
        for func in (int, float, fdim, eval):
            try:
                n = func(s)
                return n
            except:
                pass
    return s

Examples:

Python Code:

Original - Python Code
>>> convertType('31/32') 0.96875 >>> convertType('1,2,3') (1, 2, 3) >>> convertType('2.345') 2.3450000000000002 >>> convertType('2') 2 >>> convertType('[1,2,3]') [1, 2, 3] >>> convertType('[int,float,eval]') [<type 'int'>, <type 'float'>, <built-in function eval>] >>> convertType('a string') 'a string' >>>

>>> convertType('31/32')
0.96875
>>> convertType('1,2,3')
(1, 2, 3)
>>> convertType('2.345')
2.3450000000000002
>>> convertType('2')
2
>>> convertType('[1,2,3]')
[1, 2, 3]
>>> convertType('[int,float,eval]')
[<type 'int'>, <type 'float'>, <built-in function eval>]
>>> convertType('a string')
'a string'
>>>

April 15th, 2008, 11:18 AM

aamay

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Thanks folks,

I think it's even easier than that, but your examples showed me where I was going wrong. I was writing my list as [test1(), test2(),test3()] so I guess it'll all work tomorrow if I just remove the ()s.

Thanks again,
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April 15th, 2008, 12:52 PM

c-2501

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yes because the () indicate to the compiler that you wish to call the function rather than pass a pointer to it

found this function test code in a book, dont know if its quite what you're looking for but might give you some help:

Python Code:

Original - Python Code

def testit(func, *nkwargs, **kwargs):
    try:
        retval = func(*nkwargs, **kwargs)
        result = (True, retval)
    except Exception, e:
        result = (False, str(e))
    return result
 
def test():
    funcs = (int, long, float)
    vals = (1234, 12.34, '1234', '12.34')
 
    for eachFunc in funcs:
        print '-' * 20
        for eachVal in vals:
            retval = testit(eachFunc, eachVal)
            if retval[0]:
                print '%s(%s) = ' % (eachFunc.__name__, eachVal), retval[1]
            else:
                print '%s(%s) = FAILED: ' % (eachFunc.__name__, eachVal), retval[1]
 
if __name__ == '__main__':
    test()

April 15th, 2008, 09:39 PM

aamay

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I was actually thinking of something like this:

def a():
print "A"
return "OK_"

def b():
print "B"
return "ERROR"

def c():
print "C"
return "OK"

def passall(fl):
if (len(fl)):
d,f,e = fl[0]
res = f()
print d, res
if res[:len(e)]==e:
passall(fl[1:])

passall([("TryA",a,"OK"), ("TryB",b,"ERROR"), ("TryC",c,"OK")])

So that the script will give up at the first mismatch. Is there a more elegant way of getting the head and tail of the list, ideally something like declaring the parameter as f:fl like you can in haskell?

My only real problem now, is that I no longer have an excuse to use the sublime 'comefrom'.

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April 15th, 2008, 11:03 PM

bvdet

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Please use code tags. Your program structure is lost without them. Following is some suggested code:

Python Code:

Original - Python Code
def a(): print "A" return "OK_" def b(): print "B" return "ERROR" def c(): print "C" return "OK" def passall(*args): for t in args: res = t[1]() print t[0], res if t[2] != res: print 'Mismatch found' return False return True

def a():
    print "A"
    return "OK_"
 
def b():
    print "B"
    return "ERROR"
 
def c():
    print "C"
    return "OK"
 
def passall(*args):
    for t in args:
        res = t[1]()
        print t[0], res
        if t[2] != res:
            print 'Mismatch found'
            return False
    return True

Test:

Python Code:

Original - Python Code
>>> passall(("TryA",a,"OK"), ("TryB",b,"ERROR"), ("TryC",c,"OK")) A TryA OK_ Mismatch found False >>> passall(("TryA",a,"OK_"), ("TryB",b,"ERROR"), ("TryC",c,"OK")) A TryA OK_ B TryB ERROR C TryC OK True >>>

>>> passall(("TryA",a,"OK"), ("TryB",b,"ERROR"), ("TryC",c,"OK"))
A
TryA OK_
Mismatch found
False
>>> passall(("TryA",a,"OK_"), ("TryB",b,"ERROR"), ("TryC",c,"OK"))
A
TryA OK_
B
TryB ERROR
C
TryC OK
True
>>>

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