How to convert string with letters to float?

[Gordon Haag]

I am trying to do a little bit of numeric computing. I wrote a program that writes the result of each iteration of a function to a file. I want to graph these results as dots using vpython, but I am unable to do so.

I need each value to be on its own line in the text file, so I am using this to write the value to the text file:

written=str(currenttotal)
squarerootfile.write(written)
squarerootfile.write("\n")
 

currenttotal is the value produced by the function
squarerootfile is the object for the file it is written to

Then I run the text file through another program that plots the line number as the x coordinate and the value as the y coordinate. The program reads the file using this:

path="c:\\pythonfiles2\\totalsqrt32.txt"
input=file(path)
input.readline()
 

The value is returned as '0.5\n'. I need to convert this to the float 0.5. Is there a command for this? Or do I need to change the first program to not write strings? How do I do this and get it to put the next value on the next line?

Thank you,

Gordon

[bvdet]

Strings are written to and read from a file, so you are doing it correctly. You need to type cast the string you read from the file. I would suggest iteration on the file object instead of using readline(). Iteration will cease when you reach the end of the file. Use built-in function enumerate(), and you also have your line number.

fileObj = open(path)
for i, line in enumerate(fileObj):
    line_number = i
    value = float(line.strip())

[Gordon Haag]

I tried to do what you said, but the way you use i confuses me. Does 'for i, line in...' tell python that i is a line in ...? What does line.strip do?

Here is pseudo-code of what I am trying to do.

path='c:\\pythonfiles2\\totalsqrtdone.txt'
fun=file(path, "r")
line=1
while line<100000000:
    a=readline.fun(line)
    plotdot(line,a)
    line=line+1
 

The problem is that a comes back as 'a\n'.

I am using vpython to do the plotting.

I am really new to programming, all help is appreciated.

[Gordon Haag]

I figured it out.

This loop prints the way I need to:

    while abs(b**2-a)>e and steps<10000.:
        steps=steps+1
        b=(b+a/b)/2
        currenttotal=currenttotal+b
        written=currenttotal
        print>>squarerootfile, written
        print steps

This prints with \n after each entry:

    while abs(b**2-a)>e and steps<10000.:
        steps=steps+1
        b=(b+a/b)/2
        currenttotal=currenttotal+b
        written=str(currenttotal)
        squarerootfile.write(written)
        squarerootfile.write("\n")
        print steps

Now all I need to do is rerun the calculaltion.