IT, Programming, & Web Development › Forums › CS50’s Introduction to Computer Science by Harvard University on Edx › Week 6: Python › CS105: Introduction to Python by Saylor Academy › Unit 10: Object-Oriented Programming › Comparing time objects in Python: Using tuple and integer comparison in the `__lt__` method
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September 8, 2024 at 10:51 am #3425
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Here’s how you could write an
__lt__
method for aTime
class. I’ll show both approaches: one using tuple comparison, and another using integer comparison (by converting the time to total seconds).Tuple Comparison Approach
The first method compares
Time
objects using tuple comparison, similar to how we compared cards.Tuple Comparison:
class Time: def __init__(self, hours, minutes, seconds): self.hours = hours self.minutes = minutes self.seconds = seconds def __lt__(self, other): # Tuple comparison of (hours, minutes, seconds) t1 = self.hours, self.minutes, self.seconds t2 = other.hours, other.minutes, other.seconds return t1 < t2
Explanation:
- This approach compares the hours, then minutes, and then seconds in lexicographical order, ensuring that the
Time
objects are compared correctly.
Example:
time1 = Time(10, 30, 45) time2 = Time(11, 15, 20) print(time1 < time2) # True, because 10:30:45 < 11:15:20
Integer Comparison Approach
This approach converts each
Time
object to the total number of seconds since midnight and compares the resulting integers.Integer Comparison:
class Time: def __init__(self, hours, minutes, seconds): self.hours = hours self.minutes = minutes self.seconds = seconds def __lt__(self, other): # Convert each time to total seconds since midnight t1 = self.hours * 3600 + self.minutes * 60 + self.seconds t2 = other.hours * 3600 + other.minutes * 60 + other.seconds return t1 < t2
Explanation:
- We convert each time into a total number of seconds since midnight (
hours * 3600 + minutes * 60 + seconds
) and compare these integers.
Example:
time1 = Time(10, 30, 45) # 10 hours * 3600 + 30 minutes * 60 + 45 seconds time2 = Time(11, 15, 20) # 11 hours * 3600 + 15 minutes * 60 + 20 seconds print(time1 < time2) # True, because 37845 < 40520
Which Approach to Choose?
- Tuple Comparison: This is simple and expressive. Python’s built-in tuple comparison makes the code more readable, especially if you prefer to see the comparison broken down by hours, minutes, and seconds.
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Integer Comparison: This is more direct and computationally efficient if you’re frequently comparing times. It reduces the comparison to a single operation by converting the time to total seconds, which might be faster in large-scale comparisons.
Both approaches are valid depending on the context and readability versus efficiency trade-offs you want to prioritize.
- This approach compares the hours, then minutes, and then seconds in lexicographical order, ensuring that the
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