Assigning numerical IDs to variable values in a data file
You can use the Python sklearn preprocessing LabelEncoder. Here is some example code from this page with my comments:

# Make a Label Encoder instance
le = preprocessing.LabelEncoder()

# Show it the data it has to encode, so your column
le.fit(["paris", "paris", "tokyo", "amsterdam"])

# Get a ordered list of all classes it found
list(le.classes_)

# Transform a column/list
le.transform(["tokyo", "tokyo", "paris"]) 

# Transform encoding back to original
list(le.inverse_transform([2, 2, 1]))