MicroPython : Formatting Strings

Contents

• Introduction
• The Interpolation (%) Operator
  • Conversion Type
• The format() Function
  • Formatting Type
• MicroPython Tutorial Links

Introduction

The MicroPython string formatting capability is quite powerful. The MicroPython format() function closely (but not completely) aligns with the Python language standard.

All examples in this article are original and have been tested on a micro:bit for correctness using the Mu Editor.

The Interpolation (%) Operator

The Interpolation Operator (%) is built-in to operate on string objects and provides simple positional formatting. It is similar to the C language printf() style string formatting. However in the MicroPython world it is now considered old-fashioned.

In the above example the best way to describe the use of the interpolation operator is by example:

name = 'Jane'
print('My friend %s is a lawyer' %name)

          

My friend Jane is a lawyer

          

name = 'Jane'
age = 42
print('My friend %s is a lawyer. Her age is %d.' %(name, age))

            

My friend Jane is a lawyer. Her age is 42.

            

pi = 3.141593
print('The value of pi is %s to 6 decimals.' %pi)
print('The value of pi is %5.4f to 4 decimals.' %pi)
print()

BigInt = pow(9,15)
print('The big value is %d.' %BigInt)
print('The big value is %e.' %BigInt)

            

The value of pi is 3.141593 to 6 decimals.
The value of pi is 3.1416 to 4 decimals.

The big value is 205891132094649.
The big value is 2.058911e+14.

            

The format() Function

The format() method formats the specified value(s) and insert them inside the string's placeholder.

The placeholder is defined using curly brackets: {}. The placeholders can be identified using named indexes e.g. {price}, numbered indexes e.g. {0}, or even empty placeholders i.e. {}.

The format() method returns the formatted string.

This is best shown by examples

# Demonstrate string format() method

# Define some strings
pet = 'dog'
name = 'Sam'
age = 6
size = 'large'
activity = 'walking'
location = 'the park'

# format() with empty placeholders.
s1 = 'My pet is a {} and his name is {}.'.format(pet, name)

# format() with numbered indexes.
s2 = '{0} is a {1} {2} and is {3} years old.'.format(name, size, pet, age)

# format() with named indexes.
s3 = 'He enjoys {exercise} in {where}.'.format(exercise = activity, where = location)
s4 = 'We go to {where} in the {transport}.'.format(where = location, transport = 'car')

print(s1)
print(s2)
print(s3)
print(s4)

          

My pet is a dog and his name is Sam.
Sam is a large dog and is 6 years old.
He enjoys walking in the park.
We go to the park in the car.