Find and replace text based on feature class attribute

Question

I've been struggling with this problem for a few days. It seems to be more programmatic than geospatial in nature, so I'm open to suggestions to redirect this elsewhere.

I have a text file representing a project file for another program. I'm trying to search that text file based on a feature class (or shapefile) with an ID field (ATTR_1) with elevation information (ElevMeters) and replace default terrain heights with heights pulled from the feature. I can't really search for the ID info alone because it appears numerous times throughout the project file. From my perspective, I have to search through the project to find lines with $TERRAIN_HEIGHT :, look three lines above to match $PHOTO_NUM with the equivalent ATTR_1, and then replace the $TERRAIN_HEIGHT value with ElevMeters.

I've gotten my script to property assign and print correct ElevMeters values for each ATTR_1 found. I've been unable to get it to replace the $TERRAIN_HEIGHT : line properly. It prints all new values at the end of the document rather than the line I thought I was directing it to.

import os, arcpy

pdir = r"input directory path"
infile = r"input project file path"
infc = r"input feature class"
fields = ['ATTR_1', 'ElevMeters']

fpath = os.path.join(pdir, infile)
f = open(fpath, 'r+')
searchlines = f.readlines()

for i, line in enumerate(searchlines):
    if "$TERRAIN_HEIGHT : " in line:
        print i #prints line number
        for l in searchlines[i-3:i-2:2]: #go up three lines, skip every other character
            print l #prints photo_num
            print line #prints original terrain_height
            with arcpy.da.SearchCursor(infc, fields) as cursor:
                for row in cursor:
                    if str(row[0]) in l:
                        newline = str(line)[:20] + str(row[1])
                        f.write(line.replace(line, newline))
f.close()

To prove that I'm grabbing values correctly, when I run this code:

for i, line in enumerate(searchlines):
if "$TERRAIN_HEIGHT : " in line:
    print i,
    for l in searchlines[i-3:i-2:2]:
        print l,
        print line,
        with arcpy.da.SearchCursor(infc, fields) as cursor:
            for row in cursor:
                if str(row[0]) in l:
                    newline = str(line)[:20] + str(row[1])
        print newline

I get an output that looks something like this, with line number, photo number, a default $TERRAIN_HEIGHT : of 650.000000 and correct new values underneath:

...
4153   $PHOTO_NUM : 60858
  $TERRAIN_HEIGHT : 650.000000
  $TERRAIN_HEIGHT : 446.301
4165   $PHOTO_NUM : 60859
  $TERRAIN_HEIGHT : 650.000000
  $TERRAIN_HEIGHT : 447.882
4181   $PHOTO_NUM : 60860
  $TERRAIN_HEIGHT : 650.000000
  $TERRAIN_HEIGHT : 448.934
4197   $PHOTO_NUM : 60861
  $TERRAIN_HEIGHT : 650.000000
  $TERRAIN_HEIGHT : 441.156
...

Answer 1

This code will do the trick I think. It looks for any line with $PHOTO_NUM, and when it finds one it checks three lines below with the use of the linecache module. If $TERRAIN_HEIGHT : is found three lines down, the script performs a cursor to find the replacement value, and calculates the index of the line to do the replacement in. Once this index is reached the replacement is made.

I haven't tested this out on data, so there may be a coding mistake or two.

Code:

import os, arcpy, linecache

pdir = r"input directory path"
infile = r"input project file path"
infc = r"input feature class"
fields = ['ATTR_1', 'ElevMeters']

newTxtfile = r"{New\text\file\full\path}"
nf = open(newTxtfile, "w")

di = {}

fpath = os.path.join(pdir, infile)
f = open(fpath, 'r')
searchlines = f.readlines()

cur_di = {}
with arcpy.da.SearchCursor(infc, fields) as cursor:
    for row in cursor:
        cur_di[row[0]] = row[1]

for i, line in enumerate(searchlines):
    if "$PHOTO_NUM" in line: #Look for all lines with a photo number
        thirdline = linecache.getline(fpath, i + 4) #Check third line down
        if "$TERRAIN_HEIGHT :" in thirdline: #Check if terrain height is three lines down
            for key in cur_di:
                if key in line:
                    di[thirdline] = cur_di[key]    
    if i in di: #if third line down from a match
        newline = str(line)[:20] + di[i] #replace value with new
        nf.write(newline) 
    else: #else if not third line down
        nf.write(line) #write line
f.close()
nf.close()

I hope this helps!

Edit: Whoops, I forgot that you had to write everything to a new text file. Code updated. You'll have to delete the old and rename the new if you don't want the second, updated text file.

Edit2: Updated the code to work regardless of whether or not another $PHOTO_NUM occurs in the three lines between a match $PHOTO_NUM and a $TERRAIN_HEIGHT, with use of a dictionary.