Reading and writing INI files in Python (for Luke Saward)

luke.py

# Crude ini file reader/writer. Tries to retain original file formatting when writing.
# Author: Jim C K Flaten <[email protected]>

import os
import json

def parse_ini(filename, updates = {}):
    # Prepare some variables we need.
    ini = {}
    section = None

    # Open this file(s).
    r = open(filename, "r")
    w = open(filename + ".tmp", "w") if updates else None
    
    # Loop over each line.
    for raw_line in r.readlines():
        # Remove leading and trailing whitespace/special characters.
        line = raw_line.strip();
        
        # Empty line or comment.
        if not line or line[-1] == "#":
            if w: w.write(raw_line)
            continue
        
        # Section header.
        if line[:1] == "[" and line[-1] == "]":
            # We have left-over updates for the current section (new keys). Write them before entering a new section.
            if section and section in updates:
                for key in updates[section]:
                    w.write(key + "=" + str(updates[section][key]) + "\n")
                
                # End the section with an empty line for readability.
                w.write("\n")
                
                del updates[section]

            # Section name without the brackets.
            section = line[1:-1]
            
            # Initialize an empty dictionary to store this section in.
            if not section in ini.keys():
                ini[section] = {}
            
            # Copy the line "as is" if we're writing.
            if w: w.write(raw_line)
            continue

        # We've found something that's not inside a section? Skip it.
        if not section:
            # Copy the line "as is" if we're writing.
            if w: w.write(raw_line)
            continue

        # Split into key and value pair.
        pair = line.split("=")

        # Clean up the values in case there was whitespace around the equals character.
        key = pair[0].rstrip()
        value = pair[1].lstrip()
        
        # Do we have an update for this?
        if section in updates.keys() and key in updates[section].keys():
            # Pop value from the updates dict to signify that we've completed it.
            value = updates[section].pop(key)
            
            # If we're writing and the value isn't None (to be deleted), write the new value.
            if w and value != None: w.write(key + "=" + str(value) + "\n")
            
            # No more updates left in this section.
            if not updates[section]:
                del updates[section]
        elif w:
            # No update, but we're writing. Copy the line "as is".
            w.write(raw_line)

        # Store it for return, unless it was unset.
        if value != None:
            ini[section][key] = value

    # Close the read handle.
    r.close()
    
    # Close the write handle if we have one, and replace the file with our new one.
    if w:
        w.close()
        os.replace(filename + ".tmp", filename)

    return ini

#####################
# EXAMPLE USE BELOW #
#####################

# Load the current ini file.
config = parse_ini("config.ini")

# Fetch some values from the dict to look at.
authors = set(map(str.strip, config["General"]["authors"].split(",")))
rerecord_count = int(config["General"]["rerecord_count"])
flipflop = "flipflop" in config["General"];

print("Current authors are: " + ", ".join(authors))
print("Current rerecord count is: " + str(rerecord_count))
print("Current flip-flop state: " + str(flipflop))
print()

# Modify some of the data.
authors.add("Jim")                      # "Jim" will always be added to authors list, but never duplicated.
rerecord_count += 1                     # Rerecord count will increment by 1 every execution.
flipflop = None if flipflop else True   # Flip-flop will switch back and forth between not existing, and being True.

print("New authors are: " + ", ".join(authors))
print("New rerecord count is: " + str(rerecord_count))
print("New flip-flop state: " + str(flipflop))

# Create an update dict.
updates = {}
updates["General"] = {}
updates["General"]["authors"] = ", ".join(authors)
updates["General"]["rerecord_count"] = rerecord_count
updates["General"]["flipflop"] = flipflop

# Write the updates to file.
parse_ini("config.ini", updates)