Formatting Strings¶

Let us understand how we can replace placeholders in Python using different variations of formatting strings.

While we can concatenate strings, it will by default fail when we try to concatenate string with non string.
Conventionally we tend to use str to convert the data type of the non-string values that are being concatenated to string.
From Python 3, they have introduced placeholders using {} with in a string.
We can replace the placeholders either by name or by position.

Using placeholders will improve the readability of the code and it is highly recommended.

print('Hello World')

Hello World

print('Hello' + ' ' + 'World')

Hello World

# This will fail as we are trying to concatenate 0 to a string
print('Hello' + 0 + 'World')

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-3-bf74b0067f9c> in <module>
      1 # This will fail as we are trying to concatenate 0 to a string
----> 2 print('Hello' + 0 + 'World')

TypeError: must be str, not int

print('Hello' + str(0) + 'World')

Hello0World

i = 0
print('Hello' + str(i) + 'World')

Hello0World

# Replacing placeholders by name
i = 0
print(f'Hello{i}World')

Hello0World

# Replacing placeholders by name
print('Hello{i}World'.format(i=0))

Hello0World

# Replacing placeholders by position
print('Hello{}World'.format(0))

Hello0World

# Replacing placeholders by position
print('Hello{}World{}'.format(0, 1))

Hello0World1

# These are the approaches which are commonly used
i = 0
s1 = f'str1: Hello{i}World'
print(s1)
s2 = 'str2: Hello{j}World'.format(j=i)
print(s2)

str1: Hello0World
str2: Hello0World

Mastering Python

Formatting Strings¶