An iterable is an object that can provide elements one at a time. You can place it in a for loop, pass it to many functions, or use it as the source of a comprehension. section 11.1 section 11.5
Common iterable operations include:
- Iterate through strings, lists, tuples, dictionaries, files, ranges, and other supported objects without manually tracking indexes. section 11.2 section 11.5
- Transform an iterable into a list with a comprehension; use a traditional for loop when the goal is only to perform an action. section 8.2 section 8.3
- Unpack an iterable into separate function arguments by placing * before it in the call. section 2.7
- Distinguish an iterable from an iterator: an iterable supplies an iterator through __iter__, while an iterator supplies values through __next__. section 11.5
A for loop calls iter on its target, repeatedly calls next on the returned iterator, and stops when StopIteration is raised. This protocol lets different objects yield characters, keys, lines, or other values according to their own behavior. section 11.2
Joining numbers from an iterable
Convert each number while iterating, then join the resulting strings: numbers = range(15) print(','.join(str(number) for number in numbers)) The generator expression consumes numbers one at a time and avoids passing integers directly to str.join. section 8.3
Table 11.1 What you need to know
|
Concept
|
What is it?
|
Example
|
To learn more
|
|---|---|---|---|
iter
|
A built-in function that returns an object’s iterator
|
iter('abcd')
|
|
next
|
A built-in function that requests the next object from an iterator
|
next(i)
|
|
StopIteration
|
An exception raised to indicate the end of a loop
|
raise StopIteration
|
|
enumerate
|
Helps us to number elements of iterables
|
for i, c in enumerate('ab'):
print(f'{i}: {c}')
|
|
|
Iterables
|
A category of data in Python
|
Iterables can be put in
for loops or passed to many functions.
|
|
itertools
|
A module with many classes for implementing iterables
|
import itertools
|
|
range
|
Returns an iterable sequence of integers
|
# every 3rd integer, from 10
# to (not including) 50
range(10, 50, 3)
|
|
os.listdir
|
Returns a list of files in a directory
|
os.listdir('/etc/')
|
|
os.walk
|
Iterates over the files in a directory
|
os.walk('/etc/')
|
|
yield
|
Returns control to the loop temporarily, optionally returning a value
|
yield 5
|
|
os.path.join
|
Returns a string based on the path components
|
os.path.join('etc', 'passwd')
|
|
time.perf_ counter |
Returns the number of elapsed seconds (as a float) since the program was started
|
time.perf_counter()
|
|
zip
|
Takes
n iterables as arguments and returns an iterator of tuples of length
n
|
# returns [('a', 10),
# ('b', 20), ('c', 30)]
zip('abc',
[10, 20, 30])
|
Use the reference table to navigate iter, next, StopIteration, enumerate, iterables, itertools, and range. section 11.5
