Prophet for python install error log

gistfile1.txt

ValueError: Failed to parse Stan model 'anon_model_35bf14a7f93814266f16b4cf48b40a5a'. Error message:
SYNTAX ERROR, MESSAGE(S) FROM PARSER:

Illegal statement beginning with non-void expression parsed as
  gamma[i]
Not a legal assignment, sampling, or function statement.  Note that
  * Assignment statements only allow variables (with optional indexes) on the left;
    if you see an outer function logical_lt (<) with negated (-) second argument,
    it indicates an assignment statement A <- B with illegal left
    side A parsed as expression (A < (-B)).
  * Sampling statements allow arbitrary value-denoting expressions on the left.
  * Functions used as statements must be declared to have void returns


ERROR at line 33

 32:      for (i in 1:S) {
 33:        gamma[i] = -t[s_indx[i]] * delta[i];
            ^
 34:      }

PARSER EXPECTED: "}"