Create a file name using Variables in Python

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Borislav Hadzhiev

Last updated: Feb 22, 2023
3 min

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# 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.

main.py
file_name = 'example' print(f'{file_name}.txt') # ๐Ÿ‘‰๏ธ example.txt with open(f'{file_name}.txt', 'w', encoding='utf-8') as f: f.write('first line' + '\n') f.write('second line' + '\n')

create file name using variables

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

Formatted string literals (f-strings) let us include expressions inside of a string by prefixing the string with f.
main.py
var1 = 'bobby' var2 = 'hadz' result = f'{var1}{var2}.csv' print(result) # ๐Ÿ‘‰๏ธ 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.

main.py
file_name = 'example' integer = 1234 print(f'{file_name}_{integer}.txt') # ๐Ÿ‘‰๏ธ 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')

create file name that contains integer

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.

main.py
import time timestamp = int(time.time()) file_name = 'example' print(f'{file_name}_{timestamp}.txt') # ๐Ÿ‘‰๏ธ 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')

create file name with timestamp

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.

main.py
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'])

create file name using variables with addition operator

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

main.py
print('ab' + 'cd') # ๐Ÿ‘‰๏ธ abcd
However, when you use the addition operator, you have to make sure that the values on the left and right-hand sides are strings.

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

main.py
file_name = 123456 result = str(file_name) + '.csv' print(result) # ๐Ÿ‘‰๏ธ 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.

main.py
file_name = 'example' print('{}.txt'.format(file_name)) # ๐Ÿ‘‰๏ธ example.txt with open( '{}.txt'.format(file_name), 'w', encoding='utf-8' ) as f: f.write('first line' + '\n') f.write('second line' + '\n')

create file name using variables with str format

The str.format method performs string formatting operations.

main.py
first = 'bobby' last = 'hadz' result = "{}_{}.txt".format(first, last) print(result) # ๐Ÿ‘‰๏ธ "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.

main.py
first = 'bobby' last = 'hadz' result = "{f}_{l}.txt".format(f=first, l=last) print(result) # ๐Ÿ‘‰๏ธ "bobby_hadz.txt"

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

main.py
import time first = 'bobby' result = "{}_{}.txt".format(first, int(time.time())) print(result) # ๐Ÿ‘‰๏ธ "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:

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Copyright ยฉ 2024 Borislav Hadzhiev