Loop
for in statement: iterate over any sequences
The sequence can be a list,a string,a tuple and so for…
in python this statement is very very very common.
In fact for most of things we need to iterate we will use the for in
statement.
but as everything is not a sequence we generally need to transform them into sequences.
Loop with a numeric range
With the range() function,we have multiple ways:
# iterate from 0 to 2:
for i in range(3):
print("We're at time %d" % i)
# same thing but with a final step
for i in range(3):
print("We're at time %d" % i)
else:
print("final value is %d " % i)
# iterate from 2 to 9
for i in range(2, 10):
print("We're at time %d" % i)
# iterate from 0 to 9 with a step of 3 (0,3,6,9)
for i in range(0, 10, 3):
print("We're at time %d" % i) |
loop on natural sequences
on a list:
elements = ['dog', 'chicken', 'cat']
for e in elements:
print(e, len(e), 'chars') |
loop to have both the index and the value of the sequence
we can achieve it with enumerate(): a function returning a sequence under the hood
for i, v in enumerate(['tic', 'tac', 'toe']):
print(i, v) |
output:
loop on dictionary
the items() function allows to iterate both on the key and the value:
knights = {'gallahad': 'the pure', 'robin': 'the brave'}
for k, v in knights.items():
print(k, v) |
output:
gallahad the pure
robin the brave |
the keys() function allows to iterate on the keys:
knights = {'gallahad': 'the pure', 'robin': 'the brave'}
for key in knights.keys():
print(key) |
output:
the values() function allows to iterate on the values:
knights = {'gallahad': 'the pure', 'robin': 'the brave'}
for value in knights.values():
print(value) |
output:
while loop
i = 10
while i >= 5:
print(i)
i -= 1 |
To loop over two or more sequences at the same time: zip()
technically, zip() returns an iterator of tuples.
important:
in the case of the sequences don’t have the same length : the iteration finishes as soon as
the any of them is exhausted.
example:
questions = ['name', 'quest', 'favorite color']
answers = ['lancelot', 'the holy grail']
for q, a in zip(questions, answers):
print('What is your {0}? It is {1}.'.format(q, a)) |
output:
What is your name? It is lancelot.
What is your quest? It is the holy grail. |
loop in reverse on a sequence
for i in reversed(range(5)):
print(i) |
output:
loop in sorted order on a sequence
basket = ['apple', 'orange', 'apple', 'pear', 'orange', 'banana']
for i in sorted(basket):
print(i) |
output:
apple
apple
banana
orange
orange
pear |
other ways to use the sorted() function in a loop:
– sort in reverse order:
to do that we specify the reverse attribute of the function
basket = ['apple', 'orange', 'apple', 'pear', 'orange', 'banana']
for i in sorted(basket,reverse=True):
print(i) |
– specify the key to sort the elements:
to do that we specify the key attribute of the function
for example here we sort tuples by their values:
foo_tuple = {
'John': 50,
'David': 40,
}
sorted_keys = sorted(foo_tuple, key=foo_tuple.get)
print(f'sorted_keys={sorted_keys}') |
output:
sorted_keys=['David', 'John'] |
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