Python String Formatting, need to continuously add to a string

Question

I just started python, any suggestions would be greatly appreciated. I'm reading a table generated by another program and pulling out 2 numbers from each line, I'll call them a and b. (they are saved as flux and observed in my program) I need to take these two numbers from each line and format them like this-

(a,b),(a,b),(a,b) ect.

Each consecutive parenthesis is from the consecutive line, first a,b is from line 1, second a,b is from line 2, etc. I need to read the entire table however, the table length will vary.

This is what I have so far. It can read the table and pull out the numbers I need, however, I don't know how to put the numbers into the proper format. I want to say something recursive would be most efficient but I'm unsure of how to do that. Thank you in advance.

#!/usr/bin/python

file = open("test_m.rdb")

 while 1:
    line = file.readline()
    i = line.split()
    flux = i[2]
    observed = i[4]
    if not line:
        break

Do you want your data to output to a string or a list? Also, how is the input file structured? Are the two numbers separated by a space on each line, or is it like "(1,6)"? — C0deH4cker
– C0deH4cker, Commented Jun 1, 2012 at 21:43

Hugh Bothwell · Accepted Answer · 2012-06-04 14:07:30Z

1

with open("test_m.rdb") as inf:
    results = [(i[2],i[4]) for i in (line.split() for line in inf)]

result_string = ",".join(str(res) for res in results)

or a more general formatter:

result_string = ", ".join("('{2}', '{4}')".format(*res) for res in results)

edited Jun 4, 2012 at 14:07

answered Jun 1, 2012 at 21:38

Hugh Bothwell

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3 Comments

C0deH4cker Over a year ago

Do you mean result_string = ",".join([str(res) for res in results])?

Hugh Bothwell Over a year ago

@C0deH4cker - Your variant is a list comprehension, which builds a new list in memory and then passes it to join(). I wrote it as a generator expression, which passes values one at a time to join() without building a list. They both work, but mine should be slightly faster and use less memory. See python.org/dev/peps/pep-0289

C0deH4cker Over a year ago

Ahh, never knew about generator expressions like that before. Good to know, thanks!

Facundo Casco · Accepted Answer · 2012-06-01 23:07:15Z

0

Very simple solution:

with open('data') as data:
    print ', '.join('(%s, %s)' % (x.split()[2], x.split()[4])
                    for x in data.readlines())

Just use readlines to iterate over the lines in the file.

answered Jun 1, 2012 at 23:07

Facundo Casco

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Comments

Gaurav Gandhi · Accepted Answer · 2012-06-02 16:16:56Z

0

assuming that two values you got are str1 and str2
//inside a loop which iterates through your values
strTable = strTable + ['('+str1+')','('+str2+')']

hope oit will work, if it dont, comment , i will solve it.

answered Jun 2, 2012 at 16:16

Gaurav Gandhi

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1 Comment

Gaurav Gandhi Over a year ago

dont worry about commas after one set of value, it will be auto-added when adding list type values.

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