How to append float in a text file in python?

Question

So I'm a beginner in python and I was trying the append commands. It worked very well with strings but not with floats. I used this:

Num1 = float(input("Enter 1st num: "))
Num2 = float(input("Enter 2nd num: "))
Salary = num1 - num2
employee_file = open("employee_salary.txt", "a")
employee_file.write(salary)
employee_file.close()

I know I could just remove float() from input but that was just an example, my program in more complicated than that and I don't want to remove float(). Is there any command to append float to a text file? Please help me.

See What is the correct format to write float value to file in Python. — Frank from Frankfurt
– Frank from Frankfurt, Commented Jun 30, 2019 at 18:07
Text files are text. They contain strings. You can't write a float to a text file, only a string representation of a float. — BoarGules
– BoarGules, Commented Jun 30, 2019 at 18:16

Finomnis · Accepted Answer · 2019-06-30 18:11:32Z

2

You have to convert the float to a string first.

employee_file.write(str(salary))

Also, you might want to append a newline, as File.write() does not do that automatically.

employee_file.write(str(salary) + '\n')

Further, do not open and close files explicitely. It is considered better practice to do that with python's with construct:

num2 = float(input("Enter 2nd num: "))
salary = num1 - num2
with open("employee_salary.txt", "a") as employee_file:
    employee_file.write(str(salary) + '\n')
# No close necessary, the end of the with-paragraph closes the file automatically

edited Jun 30, 2019 at 18:11

answered Jun 30, 2019 at 18:05

Finomnis

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2 Comments

Devesh Kumar Singh Over a year ago

That's not off-topic, but a good advice, I would remove the words in bold if I were you

Finomnis Over a year ago

Sure, if you think that's better.

Vitor Falcão · Accepted Answer · 2019-06-30 18:06:02Z

0

You could convert it to a string and then append, use str(x) for that.

Num2 = float(input("Enter 2nd num: "))
Salary = num1 - num2
employee_file = open("employee_salary.txt", "a")
employee_file.write(str(salary))
employee_file.close()

answered Jun 30, 2019 at 18:06

Vitor Falcão

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Comments

Daweo · Accepted Answer · 2019-06-30 18:55:30Z

You need to convert your float to text to be able to write it to text file. If you are using Python 3.6 or newer you might use so-called f-strings. Just replace

employee_file.write(salary)

in your code with

employee_file.write(f"{salary}\n")

then it would always append salary and newline to your file. If you want to know more about f-strings I suggested reading this article. As side note I want to alert you that operations on floats might result in outcome, which is not correct from mathematical point of view, if you wish to read more about it there is relevant documentation piece. Due to this you might end with values less than 1 cent, in surprising places, consider following example:

s = 0.1+0.1+0.1
print(s)

Output:

0.30000000000000004

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