Python - Defining a variable without initializing, but with a value

Question

I'm working on a small task from the checkio-python coding game. It involves hard-scripting the built-in functions min() and max().

Anyway to "store" the minimal or maximal value, I thought of initializing a variable first and then store the respective lowest or highest value in it.

min_value = None
...function to compare element 1 with element 2 of a list and find lowest..
min_value = lowest_value
...function continues

When I realized that I had forgotten to compare the min_value with the lowest_value, to make sure that I would have the "globally" lowest value (of the whole list). But when I compare it, it gives me a NoneError with the first initialized variable.

 min_value = None
...function to compare element 1 with element 2 and find lowest..
if lowest_value < min_value:
 NoneError 

So how could I initialize a value without a value, which has in this case also the highest possible value, which then would change after the first comparison.

I hope, I that I was able to make my question clear.

Thanks!

Answer 1

Depend of the type of the value.

For a int, then use:

min_value = sys.maxsize

For a float, then use:

min_value = float('inf')

So any values will be smaller than those maximal numbers.

---

Alternatively, you can define the initial value with the first value of your list and iterate the list from the second value.

min_value = list[0]
for value in list[1:]:
 if value < min_value:
 min_value = value

This has the advantage to work with any type.

---

Even more alternatively, you can reduce a lambda expression like this:

min_value = reduce(lambda min_value, value: min_value if (min_value < value) else value, list)

Answer 2

Instead in initializing them as None, you can initialize them with a maximum/minimum integer value:

import sys
min_value = sys.maxsize
max_value = -sys.maxsize

Answer 3

You just have to make sure that you are not comparing to None:

mylist = [2, 5, 3, 6, 7, 4, 8]
min_value = None
for num in mylist:
 if min_value is not None and num > min_value:
 continue
 else:
 min_value = num
print "Minimum value: {0}".format(min_value)

Produces:

Minimum value: 2