# Loops

Python has two primitive loop commands:

* while loops
* for loops

### The while Loop

With the while loop we can execute a set of statements as long as a condition is true.

```
// Example
Print i as long as i is less than 6:
i = 1
while i < 6:
  print(i)
  i += 1
```

{% hint style="info" %}
**Note:** remember to increment i, or else the loop will continue forever.
{% endhint %}

The while loop requires relevant variables to be ready, in this example we need to define an indexing variable, i, which we set to 1.

### The break Statement

With the break statement we can stop the loop even if the while condition is true:

```
// Example
Exit the loop when i is 3:
i = 1
while i < 6:
  print(i)
  if i == 3:
    break
  i += 1
```

### The continue Statement

With the continue statement we can stop the current iteration, and continue with the next:

```
// Example
// Continue to the next iteration if i is 3:
i = 0
while i < 6:
  i += 1
  if i == 3:
    continue
  print(i)
```

### The else Statement

With the else statement we can run a block of code once when the condition no longer is true:

```
// Example
Print a message once the condition is false:
i = 1
while i < 6:
  print(i)
  i += 1
else:
  print("i is no longer less than 6")
```

## Python For Loops

A for loop is used for iterating over a sequence (that is either a list, a tuple, a dictionary, a set, or a string).

This is less like the for keyword in other programming languages, and works more like an iterator method as found in other object-orientated programming languages.

With the for loop we can execute a set of statements, once for each item in a list, tuple, set etc.

```
// Example
Print each fruit in a fruit list:
fruits = ["apple", "banana", "cherry"]
for x in fruits:
  print(x)
```

The for loop does not require an indexing variable to set beforehand.

### Looping Through a String

Even strings are iterable objects, they contain a sequence of characters:

```
// Example
// Loop through the letters in the word "banana":
for x in "banana":
  print(x)
```

### The break Statement

With the break statement we can stop the loop before it has looped through all the items:

```
// Example
// Exit the loop when x is "banana":
fruits = ["apple", "banana", "cherry"]
for x in fruits:
  print(x)
  if x == "banana":
    break
```

```
// Example
Exit the loop when x is "banana", but this time the break comes before the print:
fruits = ["apple", "banana", "cherry"]
for x in fruits:
  if x == "banana":
    break
  print(x)
```

### The continue Statement

With the continue statement we can stop the current iteration of the loop, and continue with the next:

```
// Example
Do not print banana:
fruits = ["apple", "banana", "cherry"]
for x in fruits:
  if x == "banana":
    continue
  print(x)
```

### The range() Function

To loop through a set of code a specified number of times, we can use the range() function,

The range() function returns a sequence of numbers, starting from 0 by default, and increments by 1 (by default), and ends at a specified number.

```
// Example
// Using the range() function:
for x in range(6):
  print(x)
```

Note that range(6) is not the values of 0 to 6, but the values 0 to 5.

The range() function defaults to 0 as a starting value, however it is possible to specify the starting value by adding a parameter: range(2, 6), which means values from 2 to 6 (but not including 6):

```
// Example
Using the start parameter:
for x in range(2, 6):
  print(x)
```

The range() function defaults to increment the sequence by 1, however it is possible to specify the increment value by adding a third parameter: range(2, 30, **3**):

```
// Example
Increment the sequence with 3 (default is 1):
for x in range(2, 30, 3):
  print(x)
```

***

### Else in For Loop

The `else` keyword in a `for` loop specifies a block of code to be executed when the loop is finished:

```
// Example
// Print all numbers from 0 to 5, and print a message when the loop has ended:
for x in range(6):
  print(x)
else:
  print("Finally finished!")
```

**Note:** The `else` block will NOT be executed if the loop is stopped by a `break` statement.

```
// Example
// Break the loop when x is 3, and see what happens with the else block:
for x in range(6):
  if x == 3: break
  print(x)
else:
  print("Finally finished!")
```

### Nested Loops

A nested loop is a loop inside a loop.

The "inner loop" will be executed one time for each iteration of the "outer loop":

```
// Example
// Print each adjective for every fruit:
adj = ["red", "big", "tasty"]
fruits = ["apple", "banana", "cherry"]

for x in adj:
  for y in fruits:
    print(x, y)
```

### The pass Statement

`for` loops cannot be empty, but if you for some reason have a `for` loop with no content, put in the `pass` statement to avoid getting an error.

```
// Example
for x in [0, 1, 2]:
  pass
```