To move through each item in a list, we use for loops
for <temporary variable> in <list>: <action>
students = ['Hanna', 'Jake', 'Jane'] for name in students: print(name) #Output: Hanna Jake Jane
The while loop is like a repeated if statement. The code is executed over and over again, as long as the condition is True. Have another look at its recipe.
while condition: # code block to be executed
nums = [0, 1, 2, 3] i = 0 while i < len(nums): print(i) i += 1 # Output 0 1 2 3
To iterate through a list of certain length, we should use
range takes in a number n as input, and returns a list from 0 to n-1.
greetings = "Hello" for i in range(2): print(greetings) # Output: Hello Hello
You can stop a for loop from inside the loop by using
When the program hits a break statement, control returns to the code outside of the for loop.
students = ['Hanna', 'Jake', 'Jane', 'April', 'Niles'] print("Find April on the list!") for name in students: if name == 'April': print(name) break print("End of search!") // Output: Find April on the list! April End of search!
If you want to skip some values while iterating through lists, we can use
For example, we’d like to print out all of the numbers in a list, unless they’re negative.
We can use continue to move to the next i in the list:
positive_list = [10, 4, -1, 2, -5, 7, 3, -9] for i in positive_list: if i < 0: continue print(i)
if we have a list made up of multiple lists, we canloop through all of the individual elements by using nested loops.
For example, create a function named exponents() return a new list containing every number in bases raised to every number in powers.
def exponents(bases, powers): new =  for i in bases: for j in powers: new.append(i**j) return new
Python list comprehensions provide a concise way for creating lists.
lst = [EXPRESSION for ITEM in LIST <if CONDITIONAL>]
# List comprehension for the squares of all even numbers between 0 and 9 result = [x**2 for x in range(10) if x % 2 == 0] print(result) # [0, 4, 16, 36, 64]
If you accidentally creates an infinite loop while developing on your own machine, you can end the loop by using
control + c to terminate the program.