Example using theano.scan to output a variable-length sequence. (Useful for e.g. generator RNNs.)

scan_variable.py

import numpy as np

import theano
import theano.tensor as T


x = T.bscalar('x')

def scan_f(x):
    # Second argument "until" establishes a stop condition
    return x + 1, theano.scan_module.until(T.eq(x, 5))

values, _ = theano.scan(scan_f, outputs_info=x, n_steps=1024)
f = theano.function([x], values)

print f(0)

# $ python scan_variable.py
# [1 2 3 4 5 6]