Introduction to iterators

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Hugo Bowne-Anderson

Data Scientist at DataCamp

Iterating with a for loop

  • We can iterate over a list using a for loop
employees = ['Nick', 'Lore', 'Hugo']

for employee in employees:
    print(employee)

Nick
Lore
Hugo
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Iterating with a for loop

  • We can iterate over a string using a for loop
for letter in 'DataCamp':
    print(letter)

D
a
t
a
C
a
m
p
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Iterating with a for loop

  • We can iterate over a range object using a for loop
for i in range(4):
    print(i)

0
1
2
3
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Iterators vs. iterables

  • Iterable
    • Examples: lists, strings, dictionaries, file connections
    • An object with an associated iter() method
    • Applying iter() to an iterable creates an iterator
  • Iterator
    • Produces next value with next()
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Iterating over iterables: next()

word = 'Da'
it = iter(word)

next(it)

'D'

next(it)

'a'

next(it)

StopIteration                   Traceback (most recent call last)
<ipython-input-11-2cdb14c0d4d6> in <module>()
-> 1 next(it)
StopIteration:
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Iterating at once with *

word = 'Data'
it = iter(word)

print(*it)

D a t a

print(*it)
  • No more values to go through!
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Iterating over dictionaries

pythonistas = {'hugo': 'bowne-anderson', 'francis': 'castro'}

for key, value in pythonistas.items():
    print(key, value)

francis castro
hugo bowne-anderson
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Iterating over file connections

file = open('file.txt')
it = iter(file)

print(next(it))

This is the first line.

print(next(it))

This is the second line.
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Let's practice!

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