According document of 'What’s New In Python 3.7', 'async' are reserved keywords now.

Code in line 105 of 'odoo/addons/base/ir/ir_qweb/assetsbundle.py' 
`def to_html(self, sep=None, css=True, js=True, debug=False, async=False, url_for=(lambda url: url)):`
will throw SyntaxError out if we launch odoo with this update python.
odoo/tools/safe_eval.py
"""expr_eval(expression) -> value
    Restricted Python expression evaluation
    Evaluates a string that contains an expression that only
    uses Python constants. This can be used to e.g. evaluate
    a numerical expression from an untrusted source.
    >>> expr_eval("1+2")
    3
    >>> expr_eval("[1,2]*2")
    [1, 2, 1, 2]
    >>> expr_eval("__import__('sys').modules")
    Traceback (most recent call last):
    ...
    ValueError: opcode LOAD_NAME not allowed
    """
    c = test_expr(expr, _EXPR_OPCODES)
    return unsafe_eval(c)
def _import(name, globals=None, locals=None, fromlist=None, level=-1):