Python: replace a string by a float in txt file

Question

Here is a problem.

I have a .py file and a .txt. To simplify, my .txt looks like:

@x@

In the .py I have

x=15

I would like to replace @x@ in the txt by the value saved in the py, ie my txt should look like

I tried with this:

for i, line in enumerate(fileinput.input('mytxtfile.txt', inplace = 1)):
    sys.stdout.write(line.replace('@x@', 'x'))

or with

for i, line in enumerate(fileinput.input('mytxtfile.txt', inplace = 1)):
    sys.stdout.write(line.replace('@x@', 'str(x)'))

The problem is that the "replace" method seems to consider only strings and I need to evaluate the value of the string. Any idea how to do it?

Thanks

S.Lott · Accepted Answer · 2011-07-22 12:05:17Z

9

The string.Template class is a good way to do this.

http://docs.python.org/library/string.html#template-strings

from string import Template
class MyTemplate( Template ): 
    delimiter= '@'
    pattern= r"@(?P<escaped>@)|@(?P<named>[_a-z][_a-z0-9]*)@|@(?P<braced>[_a-z][_a-z0-9]*)@|@(?P<invalid>)"

Given this class definition, you can now do this

with open( 'a.txt', 'r' ) as source:
    t = MyTemplate(source.read())
    result= t.substitute( x=15 )
    print result

This allows you to use any number of substitutions anywhere in the template of almost any complexity. This handles a very, very large number of cases gracefully.

answered Jul 22, 2011 at 12:05

S.Lott

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Comments

John La Rooy · Accepted Answer · 2011-07-22 11:24:08Z

7

just leave the quotes off str(x)

for i, line in enumerate(fileinput.input('mytxtfile.txt', inplace = 1)): 
    sys.stdout.write(line.replace('@x@', str(x)))

If you want more control over the output you can use a format string. Eg for 2 decimal places

for i, line in enumerate(fileinput.input('mytxtfile.txt', inplace = 1)): 
    sys.stdout.write(line.replace('@x@', "%.2f"%x))

answered Jul 22, 2011 at 11:24

John La Rooy

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4 Comments

remi Over a year ago

Thanks, I had tested it but was not using the good txt file since it had been changed from my previous try with quotes, so it didnt work :(

S.Lott Over a year ago

@remi: "not using the good txt file since it had been changed from my previous try with quotes"? What?

Cam Jackson Over a year ago

@S.Lott He had already run his incorrect code, replacing '@x@' with 'str(x)', so then when he tried to run the correct version (ie without the quotes around str(x)), it didn't work, because there weren't any @x@s in the input text file any more. That's how it reads to me, anyway.

S.Lott Over a year ago

@Cam Jackson: Guessing about their meaning is can be a bad policy. When it's confusing, I prefer to ask for clarification. I find it helpful because I learn more.

Artsiom Rudzenka · Accepted Answer · 2011-07-22 11:41:40Z

0

Not sure whether you need to replace only 'x' or there are other variables in your files, but if so than i think you can also use the following code too:

# preparing dict based on a.py
d1 = {}
for line in open('a.py','r'):
    if line.strip() and '=' in line:
        k,v = line.strip().split('=')
        d1['@' + k + '@'] = v

# preparing data from a.txt using dict from a.py
res = ''
for line in open('a.txt','r'):# lines below can be optimized depending on what you really need
    for k,v in d1.items():
        if k in line:
            line.replace(k, v)
    res += line '\n'

# write modified data
f = open('a.txt', 'w')
f.write(res.rstrip('\n'))
f.close()

answered Jul 22, 2011 at 11:41

Artsiom Rudzenka

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Comments

JooMing · Accepted Answer · 2011-07-26 18:58:57Z

0

Although you have already received nice answers to your problem, there is an alternative way. Use python formatting strings in your text files (e.g. %(x)f or %(x)s). This example shows how it works:

line = '%(x)f or %(x).2f or %(x)s'
x = 15
print line % locals()

You can use a dictionary (e.g. print line % {'x': 15}) instead of locals(). I use it as a quick and dirty way to implement templates in python.

answered Jul 26, 2011 at 18:58

JooMing

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