How can I make this function faster?

[volcano63]

with open(yaml_source) as yaml_file:
   reader = yaml.safe_load(yaml_file)
for key in value,split('.'):
    try:
        reader = reader[key]
    except (KeyError, TypeError):
        break
    return reader

i, x are terrible variable names - and your code is messy and inconsistent.

• enumerate is redundant
  
• You will never get IndexError with get
  
• Use with operator to open file
  
• PS When you get to a level that the value is not a dict - you may break out of the loop