Naming Slices in Python
The constructor of the builtin slice class creates a slice object, which can be used in places where a slice is normally employed. It is a better alternative to hardcoded slices, especially when they begin to create readability and maintenance issues.
>>> listOfNumbers = [0, 1, 2, 3, 4, 5, 6,7, 8, 9] >>> TWOtoFOUR = slice(2, 5) # Slices include elements from starting index to ending index - 1. >>> TWOtoFOUR slice(2, 5, None) # The step size is 0, hence the None. >>> listOfNumbers[TWOtoFOUR] [2, 3, 4] >>> listOfNumbers[2:5] [2, 3, 4] >>> listOfNumbers[TWOtoFOUR] = [12, 13, 14] >>> listOfNumbers [0, 1, 12, 13, 14, 5, 6, 7, 8, 9]
The slice objects provide three read-only attributes to access the indices individually. These are start, stop & step.
>>> twoToFourWithStepOne = slice(2, 5, 1) >>> twoToFourWithStepOne.start 2 >>> twoToFourWithStepOne.stop 5 >>> twoToFourWithStepOne.step 1
In addition to these attributes, it also provides a method called indices(). The indices() method is used to map a slice onto a sequence of a specific size. It takes length of the sequence as input and returns a tuple(start, stop, step) in such a manner that out of bounds indices are clipped to fit within bounds.
>>> x = slice(2, 25, 3) >>> seq = 'Hi, my name is Ethan.' >>> x.indices(len(seq)) (2, 21, 3)
See also:
- Python 101
- Object Oriented Python
- Design Patterns in Python
- 50+ Handy Standard Library Modules
- 60+ Handy Third Library Modules
- 50+ Tips & Tricks for Python Developers
- 50+ Know-How(s) Every Pythonista Must Know