Create a file name using Variables in Python

# Table of Contents

1. Create a file name using Variables in Python
2. Create a file name using Variables with the addition operator
3. Create a file name using Variables using str.format()

# Create a file name using Variables in Python

Use a formatted string literal to create a file name using variables, e.g. f'{variable}.txt'.

Formatted string literals enable us to include expressions and variables inside of a string by prefixing the string with f.

Copied!
file_name = 'example'

print(f'{file_name}.txt')  # 👉️ example.txt

with open(f'{file_name}.txt', 'w', encoding='utf-8') as f:
    f.write('first line' + '\n')
    f.write('second line' + '\n')

We used a formatted string literal to create a file name using variables.

Copied!
var1 = 'bobby'
var2 = 'hadz'

result = f'{var1}{var2}.csv'
print(result)  # 👉️ bobbyhadz.csv

Make sure to wrap expressions in curly braces - {expression}.

An advantage of f-strings is that they automatically take care of converting non-string values to strings.

# Creating a file name that contains an integer

Here is an example where we create a file name that contains an integer.

Copied!
file_name = 'example'

integer = 1234
print(f'{file_name}_{integer}.txt')  # 👉️ example_1234.txt

with open(
  f'{file_name}_{integer}.txt', 'w', encoding='utf-8'
) as f:
    f.write('first line' + '\n')
    f.write('second line' + '\n')

Formatted string literals also enable us to use expressions inside the curly braces.

# Creating a file name with a timestamp

Here is an example that uses the time.time() method to construct a file name.

Copied!
import time


timestamp = int(time.time())

file_name = 'example'

print(f'{file_name}_{timestamp}.txt')  # 👉️ example_1665817197.txt

with open(
  f'{file_name}_{timestamp}.txt', 'w', encoding='utf-8'
) as f:
    f.write('first line' + '\n')
    f.write('second line' + '\n')

We used the time.time() method to get the number of seconds since the epoch.

You can also directly call a function between the curly braces.

# Create a file name using Variables with the addition operator

An alternative approach is to use the addition (+) operator.

The addition (+) operator can be used to concatenate strings with strings stored in variables.

Copied!
import csv


file_name = 'example'

with open(
  file_name + '.csv', 'w', newline='', encoding='utf-8'
) as csvfile:
    csv_writer = csv.writer(csvfile, delimiter=',',
                            quoting=csv.QUOTE_MINIMAL)
    csv_writer.writerow(['Bobby', 'Hadz', 'Com'])

When the addition (+) operator is used with strings, it concatenates them.

Copied!
print('ab' + 'cd') # 👉️ abcd

If the variable stores an integer, use the str() class to convert it to a string.

Copied!
file_name = 123456

result = str(file_name) + '.csv'

print(result) # 👉️ 123456.csv

This is necessary because the values on the left and right-hand sides of the addition operator need to be of compatible types.

This is not the case when using f-strings because they automatically take care of the conversion for us.

# Create a file name using Variables using str.format()

You can also use the str.format() method.

The string the method is called on can contain replacement fields specified using curly braces.

Copied!
file_name = 'example'

print('{}.txt'.format(file_name))  # 👉️ example.txt

with open(
  '{}.txt'.format(file_name), 'w', encoding='utf-8'
) as f:
    f.write('first line' + '\n')
    f.write('second line' + '\n')

The str.format method performs string formatting operations.

Copied!
first = 'bobby'
last = 'hadz'

result = "{}_{}.txt".format(first, last)
print(result)  # 👉️ "bobby_hadz.txt"

The string the method is called on can contain replacement fields specified using curly braces {}.

The replacement fields can also contain the name of a keyword argument.

Copied!
first = 'bobby'
last = 'hadz'

result = "{f}_{l}.txt".format(f=first, l=last)
print(result)  # 👉️ "bobby_hadz.txt"

You can also call functions to specify a value for a replacement field.

Copied!
import time

first = 'bobby'

result = "{}_{}.txt".format(first, int(time.time()))
print(result)  # 👉️ "bobby_1665817957.txt"

Notice that the str.format() method automatically takes care of converting the integer to a string when formatting.

Which approach you pick is a matter of personal preference. I'd use a formatted string literal because I find them quite readable and intuitive.

I've also written an article on how to use f-strings for conditional formatting.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

• Split a String into multiple Variables in Python
• How to assign Print output to a Variable in Python
• Not all arguments converted during string formatting (Python)
• TypeError: Strings must be encoded before hashing (Python)
• io.UnsupportedOperation: not readable/writable Python Error
• How to clear all variables in a Python script
• How to unzip a .gz file using Python [5 simple Ways]
• How to create a Zip archive of a Directory in Python
• How to update a JSON file in Python [3 Ways]
• How to recursively delete a Directory in Python
• pygame.error: video system not initialized [Solved]