python - How to don't evaluate both functions in list choice if/else alternative? -

i'm in situation :

1. the functions contents created dynamically in string before being evaluated,
2. i don't want use if test: dosomething else: dosomethingelse compose content because users can change part of string content, , don't want them have manage spaces between math expression in conditionnal statement.

so, use following list tip: [dosomethingelse, dosomething][ test ], (true/false answser test gives me dosomething/dosomethingelse).

the solution works correctly dosomething , dosomethingelse are both evaluated before test check, , i'm interested in evaluating one. (i'm in severe time constraint situation).

is there way evaluate 1 function in 1 line ?

here, main steps of code. 'dependencies' listed here, managed in original program.

1. create unique fun_id

   def gen_id():     s = 10000     while s:         yield s         s += 1  fun_ticket = gen_id() 

2. fun descriptions (name, args, expression, id)

   from collections import defaultdict d= defaultdict(lambda :defaultdict())  d["dosomething"]["args"] = set(["arga","argb"]) d["dosomething"]["exp"] = "return arga + argb" d["dosomething"]["id"] = "f_%d"%(fun_ticket.next())  d["dosomethingelse"]["args"] = set(["argx","argy","argz"]) d["dosomethingelse"]["exp"] = "return argx + argy+ argz" d["dosomethingelse"]["id"] = "f_%d"%(fun_ticket.next())  d["dochoice"]["args"] = set(["arge","argf"]) d["dochoice"]["exp"] = "return [dosomethingelse, dosomething][arge > 0] + argf" d["dochoice"]["id"] = "f_%d"%(fun_ticket.next()) 

3. prepare dochoice function evaluated.

   dependencies =  ('dosomething', 'dosomethingelse', 'dochoice') allargs = set().union(*[d[x]["args"] x in dependencies])   funchoice = 'def %s(%s): %s'%(d['dochoice']['id'],",".join(allargs),d['dochoice']["exp"]) 

4. result: funchoice string :

   def f_10002(argx,argy,argz,arga,argb,arge,argf): return [f_10001(argx,argy,argz), f_10000(arga,argb)][arge > 0] + argf 

here problem: funchoice evaluation eval dosomething and dosomethingelse. there way eval 1 without using if else (and space management problems in string..) ?

use conditional expression:

dosomething if test else dosomethingelse 

only 1 of dosomething , dosomethingelse evaluated depending on outcome of test. quoting documentation:

the expression x if c else y first evaluates condition, c (not x); if c true, x evaluated , value returned; otherwise, y evaluated , value returned.

adapting code:

d["dochoice"]["exp"] = "return (dosomething if arge > 0 else dosomethingelse) + argf"