Copylines = []
lines.append('def print_success():')
lines.append('    print "sucesss"')
"\n".join(lines)

If you're building something complex dynamically:

Copyclass CodeBlock():
    def __init__(self, head, block):
        self.head = head
        self.block = block
    def __str__(self, indent=""):
        result = indent + self.head + ":\n"
        indent += "    "
        for block in self.block:
            if isinstance(block, CodeBlock):
                result += block.__str__(indent)
            else:
                result += indent + block + "\n"
        return result

You could add some extra methods, to add new lines to the block and all that stuff, but I think you get the idea..

Example:

Copyifblock = CodeBlock('if x>0', ['print x', 'print "Finished."'])
block = CodeBlock('def print_success(x)', [ifblock, 'print "Def finished"'])
print block

Output:

Copydef print_success(x):
    if x>0:
        print x
        print "Finished."
    print "Def finished."