Min-max python v3 implementation

Here is my implementation:

def max(*args, **kwargs): key = kwargs.get("key", lambda x: x) if len(args) == 1: args = args[0] maxi = None for i in args: if maxi == None or key(i) > key(maxi): maxi = i return maxi def min(*args, **kwargs): key = kwargs.get("key", lambda x: x) if len(args) == 1: args = args[0] mini = None for i in args: if mini == None or key(i) < key(mini): mini = i return mini 

A little bit more concise than preview post.

The issue you are having is due to the fact that min has two function signatures. From its docstring:

min(...) min(iterable[, key=func]) -> value min(a, b, c, ...[, key=func]) -> value 

So, it will accept either a single positional argument (an iterable, who's values you need to compare) or several positional arguments which are the values themselves. I think you need to test which mode you're in at the start of your function. It is pretty easy to turn the one argument version into the multiple argument version simply by doing args = args[0].

Here's my attempt to implement the function. key is a keyword-only argument, since it appears after *args.

def min(*args, key=None): # args is a tuple of the positional arguments initially if len(args) == 1: # if there's just one, assume it's an iterable of values args = args[0] # replace args with the iterable it = iter(args) # get an iterator try: min_val = next(it) # take the first value from the iterator except StopIteration: raise ValueError("min() called with no values") if key is None: # separate loops for key=None and otherwise, for efficiency for val in it: # loop on the iterator, which has already yielded one value if val < min_val min_val = val else: min_keyval = key(min_val) # initialize the minimum keyval for val in it: keyval = key(val) if keyval < min_keyval: # compare keyvals, rather than regular values min_val = val min_keyval = keyval return min_val 

Here's some testing:

>>> min([4, 5, 3, 2]) 2 >>> min([1, 4, 5, 3, 2]) 1 >>> min(4, 5, 3, 2) 2 >>> min(4, 5, 3, 2, 1) 1 >>> min(4, 5, 3, 2, key=lambda x: -x) 5 >>> min(4, -5, 3, -2, key=abs) -2 >>> min(abs(i) for i in range(-10, 10)) 0 

Functions in question have a lot in common. In fact, the only difference is comparison (< vs >). In the light of this fact we can implement generic function for finding and element, which will use comparison function passed as an argument. The min and max example might look as follows:

def lessThan(val1, val2): return val1 < val2 def greaterThan(val1, val2): return val1 > val2 def find(cmp, *args, **kwargs): if len(args) < 1: return None key = kwargs.get("key", lambda x: x) arguments = list(args[0]) if len(args) == 1 else args result = arguments[0] for val in arguments: if cmp(key(val), key(result)): result = val return result min = lambda *args, **kwargs: find(lessThan, *args, **kwargs) max = lambda *args, **kwargs: find(greaterThan, *args, **kwargs) 

Some tests:

>>> min(3, 2) 2 >>> max(3, 2) 3 >>> max([1, 2, 0, 3, 4]) 4 >>> min("hello") 'e' >>> max(2.2, 5.6, 5.9, key=int) 5.6 >>> min([[1, 2], [3, 4], [9, 0]], key=lambda x: x[1]) [9, 0] >>> min((9,)) 9 >>> max(range(6)) 5 >>> min(abs(i) for i in range(-10, 10)) 0 >>> max([1, 2, 3], [5, 6], [7], [0, 0, 0, 1]) [7]