# How to plot composition of unit step and sin functions

When i was trying to plot the function U(sin(x)) where U is the unit step function it leaves error message, but U(exp(x)) worked nicely

the error message was

```
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "_sage_input_68.py", line 10, in <module>
exec compile(u'open("___code___.py","w").write("# -*- coding: utf-8 -*-\\n" + _support_.preparse_worksheet_cell(base64.b64decode("cGxvdChoKHNpbih4KSksICh4LCAtMTAsIDEwKSk="),globals())+"\\n"); execfile(os.path.abspath("___code___.py"))
File "", line 1, in <module>
File "/tmp/tmpeAn7w2/___code___.py", line 3, in <module>
exec compile(u'plot(h(sin(x)), (x, -_sage_const_10 , _sage_const_10 ))
File "", line 1, in <module>
File "/sage/local/lib/python2.6/site-packages/sage/misc/decorators.py", line 657, in wrapper
return func(*args, **kwds)
File "/sage/local/lib/python2.6/site-packages/sage/misc/decorators.py", line 504, in wrapper
return func(*args, **options)
File "/sage/local/lib/python2.6/site-packages/sage/plot/plot.py", line 3071, in plot
G = _plot(funcs, *args, **kwds)
File "/sage/local/lib/python2.6/site-packages/sage/plot/plot.py", line 3105, in _plot
funcs, ranges = setup_for_eval_on_grid(funcs, [xrange], options['plot_points'])
File "/sage/local/lib/python2.6/site-packages/sage/plot/misc.py", line 138, in setup_for_eval_on_grid
return fast_float(funcs, *vars,**options), [tuple(range+[range_step]) for range,range_step in zip(ranges, range_steps)]
File "fast_eval.pyx", line 1388, in sage.ext.fast_eval.fast_float (sage/ext/fast_eval.c:8901)
TypeError: no way to make fast_float from None
```