Better optimization technique using if/else or dictionary

Question

Which is better optimization? - A series of if/else statement which receives the 'string' returns the appropriate function for it. (Around 40-50 if/else statements). - A dictionary maintaining the key-value pair. key as strings, and values as the function objects, and one main function to search and return the function object. The main function which actually returns the function object using above method would be called millions or billions of times, so need to do this intelligently. What could be the better way? For e.g. ``` dict['str1'] = func1 dict['str2'] = func2 and so on.. def main_func(str): return dict[str] ``` Or ``` def main_func(str): if 'str1': return func1 elif 'str2': return func2 ``` Which would be better..? if we have 50-60 such strings, and this process needs to be billions of times. Storing function object inside dictionary, in function itself:- ``` def func1(): if dict.has_key('str1'): dict['str1'] = func1 -- do something -- ``` Which is better, this or the above o…

Accepted Answer

Choose the dictionary.

The dictionary ...

- is built-in

- is pythonic

- requires less boilerplate code

- has O(1) complexity, compared to the if-else linear O(n) complexity

- isn't guilty of premature pessimization (we have insufficient reason to believe without profiling that it is a less efficient method by a large margin)

I would suggest writing the solution using a dictionary first and seeing if the solution is fast enough for your needs. If so, great, you're done. If not, time it against the other way.

Consider a solution like this (which will return `None` if the string is not found):

```
func_dict = {}
func_dict['str1'] = fun1
func_dict['str2'] = fun2
...
def function_lookup(func_string):
    return func_dict.get(func_string)
```

Then, in your main, simply write `function_lookup(whatever_string_variable)` to attempt a lookup for your function. This avoids the dictionary from being rebuilt every time `function_lookup` is called.

Better optimization technique using if/else or dictionary

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