Question

In the following code, I want to substitute the value of a string variable TotalAmount into the text document, with Python:

text_file = open("Output.txt", "w")

text_file.write("Purchase Amount: " 'TotalAmount')

text_file.close()

How to do this?

Answer 1

It is strongly advised to use a context manager. As an advantage, it is made sure the file is always closed, no matter what:

with open("Output.txt", "w") as text_file:
    text_file.write("Purchase Amount: %s" % TotalAmount)

This is the explicit version (but always remember, the context manager version from above should be preferred):

text_file = open("Output.txt", "w")
text_file.write("Purchase Amount: %s" % TotalAmount)
text_file.close()

If you’re using Python2.6 or higher, it’s preferred to use str.format()

with open("Output.txt", "w") as text_file:
    text_file.write("Purchase Amount: {0}".format(TotalAmount))

For python2.7 and higher you can use {} instead of {0}

In Python3, there is an optional file parameter to the print function

with open("Output.txt", "w") as text_file:
    print("Purchase Amount: {}".format(TotalAmount), file=text_file)

Python3.6 introduced f-strings for another alternative

with open("Output.txt", "w") as text_file:
    print(f"Purchase Amount: {TotalAmount}", file=text_file)