Question

I’ve tried to put together a solution from similar questions but have failed miserably. I just don’t know enough about Python yet 🙁

I have an inputlist containing elements in a particular order ex: ["GRE", "KIN", "ERD", "KIN"]

I have a datafile containing the elements, plus other data ex:

"ERD","Data","Data"...  
"KIN","Data","Data"...  
"FAC","Data","Data"...  
"GRE","Data","Data"...  

I need to create an outputlist that contains the lines from the datafile in the order they appear in the inputlist.

The code below returns the outputlist in the order the appear in the datafile, which is not the intended behavior… :-\

with open(inputfile, 'r') as f:
    names = [line.strip() for line in f]

outputlist = []

with open(datafile, 'r') as f:
    for line in f:
        name = line.split(',')[0]
        if name[1:-1] in names: 
            outputlist.append(line)
    output = open(outputfile, 'w')
    output.writelines(outputlist)

How can I have it return the list in the proper order? Thanks in advance for your help 🙂

Edit

Thank’s to Oscar, this is the solution I implemented:

datafile = 'C:\\testing\\bldglist.txt'
inputfile = 'C:\\testing\\inputlist.txt'
outputfile = "C:\\testing\\output.txt"

with open(inputfile, 'r') as f:
    inputlist = [line.strip() for line in f]

def outputList(inputlist, datafile, outputfile):
    d = {}
    with open(datafile, 'r') as f:
        for line in f:
            line = line.strip()
            key = line.split(',')[0]
            d[key] = line
    with open(outputfile, 'w') as f:
        f.write('"Abbrev","Xcoord","Ycoord"\n')
        for key in inputlist:
            f.write(d[key] + '\n')

outputList(inputlist, datafile, outputfile)

Answer 1

Assuming a data file with this format:

"ERD","Data","Data"...  
"KIN","Data","Data"...  
"FAC","Data","Data"...  
"GRE","Data","Data"... 

Try this solution:

def outputList(inputlist, datafile, outputfile):
    d = {}
    with open(datafile, 'r') as f:
        for line in f:
            line = line.lstrip()
            key = line.split(',')[0]
            d[key] = line
    with open(outputfile, 'w') as f:
        for key in inputlist:
            f.write(d[key])

Use it like this:

outputList(['"GRE"', '"KIN"', '"ERD"', '"KIN"'],
           '/path/to/datafile',
           '/path/to/outputfile')

It will write the output file with the expected order.