This entry explains what is a Python For Loop and how you can use it in code.
In Python, a for
loop is used to iterate over a sequence of elements. The basic syntax of a for
loop is as follows:
for variable in sequence: # Do something with the variable
Here, variable
is a new variable that takes on the value of each element in the sequence
on each iteration of the loop. The code inside the loop (indented under the for
statement) is executed once for each element in the sequence.
Looping over a range of numbers
You can use the range()
function to generate a sequence of numbers to iterate over. Here’s an example:
# Loop from 1 to 5 for i in range(1, 6): print(i)
This code will print the numbers 1 to 5, inclusive.
Looping over a string
You can use a for
loop to iterate over the characters in a string. Here’s an example:
# Loop over the characters in a string word = "hello" for letter in word: print(letter)
This code will print each character of the string “hello” on a separate line.
Looping over a list
For example, consider the following code:
fruits = ["apple", "banana", "cherry"] for fruit in fruits: print(fruit)
In this code, we define a list of fruits and then use a for
loop to iterate over the elements of the list. On each iteration of the loop, the fruit
variable takes on the value of the current fruit in the list and the print
statement is executed with that value. The output of this code would be:
apple banana cherry
Looping over a list of lists
You can use nested for
loops to iterate over a list of lists. Here’s an example:
# Loop over a list of lists matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]] for row in matrix: for value in row: print(value)
This code will print each value in the matrix on a separate line.
Looping over a dictionary
You can use a for
loop to iterate over the keys or values in a dictionary. Here are a few examples:
# Loop over the keys in a dictionary ages = {"Alice": 25, "Bob": 30, "Charlie": 35} for name in ages: print(name) # Loop over the values in a dictionary for age in ages.values(): print(age) # Loop over the key-value pairs in a dictionary for name, age in ages.items(): print(f"{name} is {age} years old")
The first loop will print the keys in the dictionary, the second loop will print the values, and the third loop will print each key-value pair.
These are just a few examples of the many ways you can use for
loops in Python to iterate over different types of sequences and data structures.