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Python break Keyword

In a Python loop, the break keyword escapes the loop, regardless of the iteration number. Once break executes, the program will continue to execute after the loop.

In this example, the output would be:

  • 0
  • 254
  • 2
  • Negative number detected!
numbers = [0, 254, 2, -1, 3] for num in numbers: if (num < 0): print("Negative number detected!") break print(num)

Python List Comprehension

Python list comprehensions provide a concise way for creating lists. It consists of brackets containing an expression followed by a for clause, then zero or more for or if clauses: [EXPRESSION for ITEM in LIST <if CONDITIONAL>].

The expressions can be anything - any kind of object can go into a list.

A list comprehension always returns a list.

# 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]

The Python continue Keyword

In Python, the continue keyword is used inside a loop to skip the remaining code inside the loop code block and begin the next loop iteration.

big_number_list = [1, 2, -1, 4, -5, 5, 2, -9] # Print only positive numbers: for i in big_number_list: if i < 0: continue print(i)

Python for Loops

Python for loops can be used to iterate over and perform an action one time for each element in a list.

Proper for loop syntax assigns a temporary value, the current item of the list, to a variable on each successive iteration: for <temporary value> in <a list>:

for loop bodies must be indented to avoid an IndentationError.

dog_breeds = ["boxer", "bulldog", "shiba inu"] # Print each breed: for breed in dog_breeds: print(breed)

Python Loops with range().

In Python, a for loop can be used to perform an action a specific number of times in a row.

The range() function can be used to create a list that can be used to specify the number of iterations in a for loop.

# Print the numbers 0, 1, 2: for i in range(3): print(i) # Print "WARNING" 3 times: for i in range(3): print("WARNING")

Python Loop

Remember, a loop always visits items in sequential order. This means it will visit every item in start from finish every time.

The first line of code will print 1 - 4. The next one will print 4- 1. What matters is the order of the values within the list, not their size.

list1 = [1,2,3,4] for i in list1: print(i) list2 = [4,3,2,1] for i in list2: print(i)

Python while Loops

In Python, a while loop will repeatedly execute a code block as long as a condition evaluates to True.

The condition of a while loop is always checked first before the block of code runs. If the condition is not met initially, then the code block will never run.

# This loop will only run 1 time hungry = True while hungry: print("Time to eat!") hungry = False # This loop will run 5 times i = 1 while i < 6: print(i) i = i + 1

Python Nested Loops

In Python, loops can be nested inside other loops. Nested loops can be used to access items of lists which are inside other lists. The item selected from the outer loop can be used as the list for the inner loop to iterate over.

groups = [["Jobs", "Gates"], ["Newton", "Euclid"], ["Einstein", "Feynman"]] # This outer loop will iterate over each list in the groups list for group in groups: # This inner loop will go through each name in each list for name in group: print(name)