Created Radiation, Photo classes and slimmed down main program.

- Radiation creates a list with timezone_aware datetime and radiation in µS/h.
- Photo reads DateTimeOriginal from photo.
- Photo.write_exif compiles new metadata object and writes exif tags to photo.
- Documentd changes in CHANGELOG.md.
- Changed Readme.me to match changes in code.
- Removed obsolete line from .gitignore

functions.py

@@ -1,14 +1,16 @@
 #!/usr/bin/env python
 # -*- coding: utf-8 -*-
 
-"""Classes used by main program. Handles CSV and GPX processing."""
+''' Classes used by main program. '''
 
 from datetime import datetime
+import pyexiv2
 
 class Radiation:
+    ''' Handles CSV processing.'''
     def __init__(self, timestamp, radiation, local_timezone, si_factor):
         self.timestamp = self._time_conversion(timestamp, local_timezone)
-        self.radiation = self._radiation(radiation, si_factor)
+        self.radiation = self._radiation_conversion(radiation, si_factor)
 
     def __repr__(self):
         return '%s %f µS/h' % (str(self.timestamp), self.radiation)
@@ -19,7 +21,49 @@ class Radiation:
         csv_aware_time = csv_naive_time.astimezone(local_timezone)
         return csv_aware_time
 
-    def _radiation(self, radiation, si_factor):
+    def _radiation_conversion(self, radiation, si_factor):
         # Convert CP/M to µS/h using si_factor
         radiation = round(float(radiation) * si_factor, 2)
         return radiation
+
+class Photo:
+    ''' Reads and writes Exif metadata'''
+    def __init__(self, photo, local_timezone):
+        self.get_date = self._get_creation_date(photo, local_timezone)
+        self.photo = photo
+
+    def __repr__(self):
+        return 'Photo Creation Date: %s' % str(self.get_date)
+
+    def _get_creation_date(self, photo, local_timezone):
+        # Load Exif data from photo
+        metadata = pyexiv2.ImageMetadata(photo)
+        metadata.read()
+        date = metadata['Exif.Photo.DateTimeOriginal']
+        # date.value creates datetime object in pic_naive_time
+        pic_naive_time = date.value
+        # Set timezone
+        pic_aware_time = pic_naive_time.astimezone(local_timezone)
+        return pic_aware_time
+
+    def write_exif(self, radiation, latitude, longitude, dry_run):
+
+        ''' UNTESTED ! '''
+
+        metadata = pyexiv2.ImageMetadata(self.photo)
+        
+        # Set new UserComment
+        new_comment = 'Radiation ☢ ' + str(radiation) + ' µS/h'
+        # Exif tags to write
+        keys = ['Exif.Photo.UserComment', 'Exif.Photo.latitude', 'Exif.Photo.longitude']
+        # Values to write
+        values = [new_comment, latitude, longitude]
+        
+        # Create metadata object with all data to write
+        for key, value in zip(keys, values):
+            metadata[key] = pyexiv2.ExifTag(key, value)
+
+        # Write Exif tags to file, if not in dry-run mode
+        if dry_run == 'True':
+            metadata.write()
+        return new_comment