What is the point of float('inf') in Python?

后端 未结 5 1788
滥情空心
滥情空心 2020-12-02 16:26

Just wondering over here, what is the point of having a variable store an infinite value in a program? Is there any actual use and is there any case where it would be prefer

相关标签:
5条回答
  • 2020-12-02 16:57

    From the documentation:

    Many floating-point features were added. The float() function will now turn the string nan into an IEEE 754 Not A Number value, and +inf and -inf into positive or negative infinity. This works on any platform with IEEE 754 semantics. (Contributed by Christian Heimes; issue 1635.)

    Also refer this: Working with Infinity and NaNs

    0 讨论(0)
  • 2020-12-02 16:58

    float('inf') can be used in the comparison, thus making the code simpler and clear. For instance, in merge sort, a float('inf') can be added to the end of subarrays as a sentinel value. Don't confuse with the usage of infinity in maths, after all, programming is not all about maths.

    0 讨论(0)
  • 2020-12-02 17:05
    float('inf')
    

    As stated in answer above, float('inf') is used for setting a variable with an infinitely large value. In simple words, it sets the value as +ve infinty.

    ALTERNATIVELY, we can make use of the following statement,

    import sys
    least_value = sys.maxsize
    

    The sys.maxsize is more commonly used, for setting large value initially. When our aim is to find the least value from given set of values.

    Also, in case if we want to find largest value from given set of values. We can use the following.

    import sys
    greatest_value = -sys.maxsize - 1
    
    # logic for comparing with rest of values
    

    The -sys.maxsize - 1 is used for setting initial value as -ve infinity.

    0 讨论(0)
  • 2020-12-02 17:06

    It acts as an unbounded upper value for comparison. This is useful for finding lowest values for something. for example, calculating path route costs when traversing trees.

    e.g. Finding the "cheapest" path in a list of options:

    >>> lowest_path_cost = float('inf')
    >>> # pretend that these were calculated using some worthwhile algorithm
    >>> path_costs = [1, 100, 2000000000000, 50]
    >>> for path in path_costs:
    ...   if path < lowest_path_cost:
    ...     lowest_path_cost = path
    ...
    >>> lowest_path_cost
    1
    

    if you didn't have float('Inf') available to you, what value would you use for the initial lowest_path_cost? Would 9999999 be enough -- float('Inf') removes this guesswork.

    0 讨论(0)
  • 2020-12-02 17:11

    Instead of using 0 and then you need to handle negative numbers if there is any, float("+inf") and float("-inf") help compare positive or negative infinity like:

    Find the largest value in a dictionary:

    def max_key(my_dict):
        largest_key = float("-inf")
        largest_value = float("-inf")
    
        for key, value in my_dict.items():
          if value > largest_value:
              largest_value = value
              largest_key = key
        return largest_key
    
    
    print(max_key({1:100, 2:1, 3:4, 4:10}))      # should print 1
    
    print(max_key({"a":100, "b":10, "c":1000}))  # should print "c"
    
    0 讨论(0)
提交回复
热议问题