CODEWITHSUNDEEP
pythonpython-2.7
yirueilu
yirueilu

Reputation: 43

How to write a function keeping return the maximum value while calling it repeatedly

I am learning Python and practice some problem on the book.

The problem asks me to write a function keeping the max value.

The function (foo) works like below:

I don't know what is the key point of this problem.

Upvotes: 1

Views: 524

Answers (3)

user5538922
user5538922

Reputation:

In mathematics, if a function is given certain input, it always returns the same value. That is what pure(sorry about being vague in wording) functions do. It means, your function will forget every information it used once it's done its job. In this case, your functions is not likely to remember previous max value and you will not be able to solve your problem, right? That's why other people suggested somewhat complex solutions like global variables or class. They do different jobs but they are all about keeping previous state(or what happened in the past). I would suggest one more method to achieve your goal. This may seem harder for now, but you will appreciate this later.

# written in Python3, not Python2
def function_factory():
    prev_max = None
    def print_max(num):
        nonlocal prev_max
        # prev_max is None or smaller than num
        if not (prev_max and prev_max > num):
            prev_max = num
        print(prev_max)
    return print_max

# make an instacne of print_max and bind that
# new function to the name, my_func
my_func = function_factory()
my_func(3)  # >> 3
my_func(5)  # >> 5
my_func(3)  # >> 5

I used what's called a closure, and if you are interested you can study functional programming. It's a bit involved but makes your code succinct.

Upvotes: 1

KromviellBlack
KromviellBlack

Reputation: 918

Another way (and much more correct in terms of encapsulation for the production code) to complete the task is to use classes instead of functions and global variables:

class MaxPositiveValue:
    def __init__(self):
        self.max_value = 0

    def __call__(self, new_value):
        '''
        This magic method will emulate function call
        :param new_value: new value to compare
        :return: max value
        '''
        if new_value > self.max_value:
            self.max_value = new_value
        return self.max_value

foo = MaxPositiveValue()
print(foo(1))  # Will print "1"
print(foo(5))  # Will print "5"
print(foo(2))  # Will print "5"
print(foo(10))  # Will print "10"
print(foo(4.6))  # Will print "10"
print(foo(12.8))  # Will print "12.8"

And if you want to properly compare both positive and negative numbers, you may use next code:

class MaxValue:
    def __init__(self):
        self.max_value = None

    def __call__(self, new_value):
        '''
        This magic method will emulate function call
        :param new_value: new value to compare
        :return: max value
        '''
        if (self.max_value is None) or (new_value > self.max_value):
            self.max_value = new_value
        return self.max_value

foo = MaxValue()
print(foo(-10.4))  # Will print "-10.4"
print(foo(-30.1))  # Will print "-10.4"
print(foo(1))  # Will print "1"
print(foo(5.6))  # Will print "5.6"
print(foo(2))  # Will print "5.6"
print(foo(10))  # Will print "10"

Upvotes: 5

AER
AER

Reputation: 1531

Your question is about global variables. It is saying to create a variable that is not dependent upon that instance of the function. Instance is used (in this case) to describe when that function is being used. Setting the variable as a global keeps it as that value irrespective of being in a different time the function has been called.

This code would be the solution:

glob_max = 0 #This variable needs to be set before the function 
    #(assuming you're just using natural numbers otherwise set a smaller number)

def foo(numbr):
    if numbr > glob_max: #This find if it is the max or not
        glob_max = numbr #Sets the variable
    global glob_max #Makes the variable global to remember it for other functions
    print(glob_max) #Print the number as required

Upvotes: 0

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