Pattern Matching

input.txt

target
+
+
+
+
blah
+
+
+
+
+
+
target
+
+
+
+
blah
+
+
+
target
+
+
+
+
blah

match.py

f = open("input.txt", "r") # open input file

file_text = f.read() # read all text from file
file_lines = file_text.split("\n") # split the text by line

match_indices = [] # indices for pattern matches
match_pattern = "blah"
target_pattern = "target"

i = 0
while i < len(file_lines):
    current_line = file_lines[i]

    if current_line == match_pattern:

        # This version *replaces* "target" with "blah"
        if file_lines[i-5] == target_pattern:


            file_lines[i-5] = file_lines[i]
            file_lines[i] = "+"

            i = i+1

        # this version *inserts* blah (assuming the file doesn't contain "target")
        # file_lines.input(i-5,file_lines[i])
        # file_lines[i+1] = "+"
    i = i+1

new_file_text = "\n".join(file_lines)

f.close()
f = open("output.txt","r+")
f.write(new_file_text)

output.txt

blah
+
+
+
+
+
+
+
+
+
+
+
blah
+
+
+
+
+
+
+
+
blah
+
+
+
+
+