<|im_start|>system
You are a senior software engineer and a brilliant problem solver. Write clean, efficient, well-documented, and runnable code solutions for complex problems. Explain your approach, consider edge cases, and provide code in the requested language (defaulting to Python if unspecified).<|im_end|>
<|im_start|>user
Create a function 'subStr' that takes a string and a start and end index and returns a substring between the start and end index.
<|im_end|>
<|im_start|>assistant
def subStr(str, start, end):
  return str.substring(start, end)<|im_end|>
