Dictionary Functions: What does max () return for dictionaries?

The max function accepts any iterated object, returns the maximum of its elements. If you iterate a dictionary with for , for example, you get a sequence of its keys, so the max function will return the maximum of the keys. For lines in python, the one that is later in the lexicographical (alphabetical) order is considered the most. In the first case, the maximum key will be 'd' , in the second 'v' .

In general, for objects for which you need to find the maximum (without using the key argument of the max function, about it below), a more-less ratio should be defined. For your classes, you must at least define the __lt__() method:

 >>> class A(): ... def __init__(self, value): ... self.value = value ... ... def __lt__(self, other): ... return self.value > other.value # Знак больше вместо меньше вставлен намеренно ... ... def __repr__(self): ... return 'A(%r)' % self.value >>> max([A(1), A(2), A(3)]) A(1) 

To get the maximum on some basis (not the way the comparison is determined for specific objects), you can use the key argument of the max function. Through this argument, you can pass a function that will return the parameter by which you want to make a comparison. A typical example is to find the maximum length:

 s = ['abc', 'ab', 'def', 'dead'] print(max(s)) # максимум по алфавиту - 'def' print(max(s, key=len)) # максимум по длине - 'dead' 

Another fairly typical case is a list of tuples, you need to select a maximum of one of the fields of the tuple:

 s = [(1, 10), (2, 9), (3, 8), (4, 7), (5, 6), (6, 5), (7, 4), (8, 3), (9, 2), (10, 1)] # находим максимальный элемент списка по значению первого элемента кортежа: print(max(s, key=lambda x: x[0])) # выведет (10, 1) # находим максимальный элемент списка по значению второго элемента кортежа: print(max(s, key=lambda x: x[1])) # выведет (1, 10)