about a discussion at pycon and the existence of a «secured reduced shell»

aval.py

#!/usr/bin/env python
def aval(xstr):
    """ eval a string with all builtins from the interpreter forbidden & no
    globals"""
    print "".join(["*" * 20, "<", xstr, ">", "*" * 20])
    try:
        print "'safe' EVAL"
        print eval( xstr,{'__builtins__':{}},{})
    except Exception as e:
        print "!%s not usable %r" % (xstr,e)
        pass
    print "\n"

t = lambda *p:"\n".join(list(p) + [ "*" *80, "" ])
print t("problematic")
aval("""[
    c for c in ().__class__.__base__.__subclasses__() if c.__name__ == 'catch_warnings'
    ][0]()._module.__builtins__""")

print t("more problematic")
aval("[ i * 2  for i in 'lklmk']")
aval(""" ";)" *100 """)

aval(""" "%2000000.200000f" % 0.0 """)
aval("""len( "%2000000.200000f" % 0.0) """)
aval(""" (2**2**2**2**2).__sizeof__()""")