How long does the Collatz recursion run? I have the following Python code.

def collatz(n):
    if n &lt;= 1:
        return True
    elif (n%2==0):
        return collatz(n/2)
    else:
        return collatz(3*n+1)


What is the running-time of this algorithm?

Try: 

If $T(n)$ denotes the running time of the function collatz(n). Then I think I have 
\begin{cases}
T(n)=1 \text{ for } n\le 1\\
T(n)=T(n/2) \text{ for } n\text{ even}\\
T(n)=T(3n+1) \text{ for } n\text{ odd}\\
\end{cases}

I think $T(n)$ will be $\lg n$ if $n$ is even but how to calculate the recurrence in general?
This is Collatz conjecture - still open problem.
Conjecture is about proof that this sequence stops for any input, since this is unresolved, we do not know how to solve this runtime recurrence relation, moreover it may not halt at all - so until proven, the running time is unknown and may be $\infty$.