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Python BlockBuilt-in Functions


enumerate, reversed, sorted, zip

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Python Built-in Conversion Functions
enumerate()
  Parameters
  Remarks
reversed()
  Parameters
  Remarks
sorted()
  Parameters
  Remarks
zip()
  Parameters
  Remarks
 Source and Reference

Python Built-in Conversion Functions

The Python interpreter has some built-in conversion functions.

enumerate()

enumerate(iterable, start=0)

Parameters

type()to return an enumerate object. iterableto specify the iterable be returned from start=0to specify the starting number

Remarks

  • iterable must be a sequence, an interator, or some other object which supports iteration.
  • The __next__() method of the iterator returned by enumerate() returns a tuple containing a count (from start which defaults to 0) and the values obtained from iterating over iterable.
  • Equivalent to: def enumerate(sequence, start=0): n = start for elem in sequence: yield n, elem n += 1

reversed()

reversed(seq)

Parameters

reversed()to return a reverse iterator. seqto specify the seq to be returned from

Remarks

  • Return a reverse iterator. seq must be an object which has a __reversed__() method or supports the sequence protocol (the __len__() method and the __getitem__() method with integer arguments starting at 0).

sorted()

sorted(iterable, *, key=None, reverse=False)

Parameters

sorted()to return a new sorted list from element of iterable. iterableto specify the iterable to be returned from * key=Noneto specify the comparison key to be used. reverse=Falseto specify the sorting method.

Remarks

  • Return a new sorted list from the items in iterable. Has two optional arguments which must be specified as keyword arguments. key specifies a function of one argument that is used to extract a comparison key from each element in iterable (for example, key=str.lower). The default value is None (compare the elements directly). reverse is a boolean value. If set to True, then the list elements are sorted as if each comparison were reversed. Use functools.cmp_to_key() to convert an old-style cmp function to a key function. The built-in sorted() function is guaranteed to be stable. A sort is stable if it guarantees not to change the relative order of elements that compare equal — this is helpful for sorting in multiple passes (for example, sort by department, then by salary grade).

zip()

zip(*iterables)

Parameters

zip()to return an iterator of tuples. *iterablesto specify the iterables to be returned from.

Remarks

  • Make an iterator that aggregates elements from each of the iterables. Returns an iterator of tuples, where the i-th tuple contains the i-th element from each of the argument sequences or iterables. The iterator stops when the shortest input iterable is exhausted. With a single iterable argument, it returns an iterator of 1-tuples. With no arguments, it returns an empty iterator. Equivalent to: def zip(*iterables): # zip('ABCD', 'xy') --> Ax By sentinel = object() iterators = [iter(it) for it in iterables] while iterators: result = [] for it in iterators: elem = next(it, sentinel) if elem is sentinel: return result.append(elem) yield tuple(result) The left-to-right evaluation order of the iterables is guaranteed. This makes possible an idiom for clustering a data series into n-length groups using zip(*[iter(s)]*n). This repeats the same iterator n times so that each output tuple has the result of n calls to the iterator. This has the effect of dividing the input into n-length chunks. zip() should only be used with unequal length inputs when you don’t care about trailing, unmatched values from the longer iterables. If those values are important, use itertools.zip_longest() instead. zip() in conjunction with the * operator can be used to unzip a list:

Source and Reference


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ID: 200602302 Last Updated: 23/6/2020 Revision: 0

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