4.3. Formatting Strings
In this section, we'll discuss some ways of formatting strings.
Concatenating strings
Two strings can be added to produce a new joined string.
string1 = 'Hello'
string2 = 'World'
print(string1 + ' ' + string2)
Hello World
Note that a string can only be added to a string. If we add another data type to a string, an error is raised:
to_add = 1
print('Hello' + to_add)
Traceback (most recent call last):
File "G:\thepyguide\main.py", line 2, in <module>
print('Hello' + to_add)
~~~~~~~~^~~
TypeError: can only concatenate str (not "int") to str
The right way of doing this is to convert the value to be added to string before addition:
to_add = 1
print('Hello' + str(to_add))
Hello1
The format() method
The format() method is used to format a string and include variable values to it.
name = input('Enter your name: ')
nickname = input('Enter your nickname: ')
greeting = 'Hello, {}. I will call you {} from now'.format(name, nickname)
print(greeting)
Enter your name: John
Enter your nickname: Jay
Hello, John. I will call you Jay from now
{} placeholder is replaced with the arguments provided to format() method. Note the order
is important. The first argument is substituted with first {} in the string and
vice versa.
Changing placeholders order
To change the order, the indexes can be used:
name = input('Enter your name: ')
nickname = input('Enter your nickname: ')
greeting = 'Hello, {1}. I will call you {0} from now'.format(name, nickname)
print(greeting)
Enter your name: John
Enter your nickname: Jay
Hello, Jay. I will call you John from now
Here, {1} is replaced with second argument and {0} is replaced with first argument.
Different data types
Unlike concatenating strings, the arguments in format() are automatically converted
to string and don't have to be of str data type.
n1 = int(input('Enter first number: '))
n2 = int(input('Enter second number: '))
product = n1 * n2
print('The product is: {}'.format(product))
Enter first number: 20
Enter second number: 3
The product is 60.
Named placeholders
The curly brackets could include an identifier name which would be used while formatting the string.
template = 'Hello, {real_name}. I will call you {nick} from now'
name = input('Enter your name: ')
nickname = input('Enter your nickname: ')
print(template.format(real_name=name, nick=nickname))
Hello, John. I will call you Jay from now.
f-string
f-string is a more convenient method of formatting. It is clearer and more readable than
the format() method.
To use an f-string, f is placed before the opening quote of a string and variables
or values to include in strings are put in curly brackets.
name = input('Enter your name: ')
nickname = input('Enter your nickname: ')
greeting = f'Hello, {name}. I will call you {nickname} from now'
print(greeting)
Enter your name: John
Enter your nickname: Jay
Hello, John. I will call you Jay from now
Similar to format, the values inside curly brackets could be of any data type and would automatically be converted to string.
Expressions could also be used:
n1 = int(input('Enter first number: '))
n2 = int(input('Enter second number: '))
print(f'The product is: {n1 * n2}')
Enter first number: 20
Enter second number: 3
The product is: 60