Question

So, I’m trying to write a random amount of random whole numbers (in the range of 0 to 1000), square these numbers, and return these squares as a list. Initially, I started off writing to a specific txt file that I had already created, but it didn’t work properly. I looked for some methods I could use that might make things a little easier, and I found the tempfile.NamedTemporaryFile method that I thought might be useful. Here’s my current code, with comments provided:

# This program calculates the squares of numbers read from a file, using several functions
# reads file- or writes a random number of whole numbers to a file -looping through numbers
# and returns a calculation from (x * x) or (x**2);
# the results are stored in a list and returned.
# Update 1: after errors and logic problems, found Python method tempfile.NamedTemporaryFile: 
# This function operates exactly as TemporaryFile() does, except that the file is guaranteed to   have a visible name in the file system, and creates a temprary file that can be written on and accessed 
# (say, for generating a file with a list of integers that is random every time).

import random, tempfile 

# Writes to a temporary file for a length of random (file_len is >= 1 but <= 100), with random  numbers in the range of 0 - 1000.
def modfile(file_len):
       with tempfile.NamedTemporaryFile(delete = False) as newFile:
            for x in range(file_len):
                 newFile.write(str(random.randint(0, 1000)))
            print(newFile)
return newFile

# Squares random numbers in the file and returns them as a list.
    def squared_num(newFile):
        output_box = list()
        for l in newFile:
            exp = newFile(l) ** 2
            output_box[l] = exp
        print(output_box)
        return output_box

    print("This program reads a file with numbers in it - i.e. prints numbers into a blank file - and returns their conservative squares.")
    file_len = random.randint(1, 100)
    newFile = modfile(file_len)
    output = squared_num(file_name)
    print("The squared numbers are:")
    print(output)

Unfortunately, now I’m getting this error in line 15, in my modfile function: TypeError: 'str' does not support the buffer interface. As someone who’s relatively new to Python, can someone explain why I’m having this, and how I can fix it to achieve the desired result? Thanks!

EDIT: now fixed code (many thanks to unutbu and Pedro)! Now: how would I be able to print the original file numbers alongside their squares? Additionally, is there any minimal way I could remove decimals from the outputted float?

Answer 1

You need to put newlines after each int, lest they all run together creating a huge integer:

newFile.write(str(random.randint(0, 1000))+'\n')

(Also set the mode, as explained in PedroRomano’s answer):

   with tempfile.NamedTemporaryFile(mode = 'w+', delete = False) as newFile:

---

modfile returns a closed filehandle. You can still get a filename out of it, but you can’t read from it. So in modfile, just return the filename:

   return newFile.name

And in the main part of your program, pass the filename on to the squared_num function:

filename = modfile(file_len)
output = squared_num(filename)

---

Now inside squared_num you need to open the file for reading.

with open(filename, 'r') as f:
    for l in f:
        exp = float(l)**2       # `l` is a string. Convert to float before squaring
        output_box.append(exp)  # build output_box with append

---

Putting it all together:

import random, tempfile 

def modfile(file_len):
       with tempfile.NamedTemporaryFile(mode = 'w+', delete = False) as newFile:
            for x in range(file_len):
                 newFile.write(str(random.randint(0, 1000))+'\n')
            print(newFile)
       return newFile.name

# Squares random numbers in the file and returns them as a list.
def squared_num(filename):
    output_box = list()
    with open(filename, 'r') as f:
        for l in f:
            exp = float(l)**2
            output_box.append(exp)
    print(output_box)
    return output_box

print("This program reads a file with numbers in it - i.e. prints numbers into a blank file - and returns their conservative squares.")
file_len = random.randint(1, 100)
filename = modfile(file_len)
output = squared_num(filename)
print("The squared numbers are:")
print(output)

---

PS. Don’t write lots of code without running it. Write little functions, and test that each works as expected. For example, testing modfile would have revealed that all your random numbers were being concatenated. And printing the argument sent to squared_num would have shown it was a closed filehandle.

Testing the pieces gives you firm ground to stand on and lets you develop in an organized way.