7.2. Looping - JulTob/Python GitHub Wiki

In Python, we can iterate in different forms.

🐍 While Looping

🐊 While the statement is True, the code inside the block will be executed

while <TestExpression>:       0 to ∞ times
    <Block>
Romani_ite_domum = 1
while Romani_ite_domum <= 100:
    print("Romani ite domum")
    Romani_ite_domum += 1
print("And don't do it again")
loop_condition = True

while loop_condition:
    print("Loop Condition True")
    loop_condition = False
else:
    print("Loop Condition False")

πŸ¦– The loop condition is True so it keeps iteratingβ€Šβ€”β€Šuntil we set it to False.

i=0
while i<10:
    print i
    i= i+1
def print_numbers(n):
    i=1
    while i<=n:
        print i
        i= i+1
def factorial(n):
    fact=1
    i=1
    while i<=n:
        fact=i*fact
        i= i+1
    return fact

🐒 While Break

while <TestExpression>:       0 to ∞ times
    <Block>
    if <BreakTest>:
        break
while True:
  s = input('Enter something : ')
  if s == 'quit':
    break
  print('Length of the string is', len(s))
print('Done')

πŸ’« For Looping

🌘 Iterates over defined ranges.

for i in 1, 2, 3, 4, 5, 6, 7, 8, 9, 10:
   print(i)

for i in range(1, 100):  #  1 .. 99
   print(i)

for i in range(1, 100, 2):   #  1, 3, 5, ..+2.. , 96, 99 
   print(i)

for i in range(100):   #  0 .. 99
   print(i)

for i in range(1, -100, -1):   #  1 , 0, -1 .. -99 
   print(i)

for i in range(21, 0, -3)
   print(n, end=' ')
# 21 18 15 12 9 6 3

primes = [2, 3, 5, 7]
for number in primes:
    print(number)
for c in β€œword”:
   print(c)     
> w
> o
> r
> d

β˜„οΈ Break

Terminates loop.

πŸͺ Continue

Skip iteration.

⭐️ Pass

Null statement.

for i in range(100):   #  0 .. 100
    if  i % 4 = 0:
        continue
    print(i )
    if  i  > 90:
        break
for n in numbers:
    if n % 2 == 0:
            print (n)
    if n == 237:
            break

Code that modifies a collection while iterating over that same collection can be tricky to get right. Instead, it is usually more straight-forward to loop over a copy of the collection or to create a new collection:

# Strategy:  Iterate over a copy
for user, status in users.copy().items():
    if status == 'inactive':
        del users[user]

# Strategy:  Create a new collection
active_users = {}
for user, status in users.items():
    if status == 'active':
        active_users[user] = status
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