python - Python值转换为postgres过程参数的字符串表示，包括类型转换

Question

我正在尝试寻找具有以下内容的方法：

IN: <SOME_PYTHON_VALUE>
OUT: val::type_cast

和...

IN: [<SOME_PYTHON_VAL>,<SOME_PYTHON_VAL>]
OUT: '{val,val}'::type_cast[]

Answer 1

'''
    >>> py_to_pg([1,2,3])
    "'{1,2,3}'::int[]"
    >>> py_to_pg('Jack Johnson')
    "'Jack Johnson'::text"
    >>> py_to_pg([decimal.Decimal(0.3),decimal.Decimal(0.3),decimal.Decimal(0.4)])
    "'{0.3,0.3,0.4}'::numeric(5,4)[];"
    >>> py_to_pg(datetime.datetime(2013,7,7,13,0,0))
    "'2013-07-07T13:00:00'::timestamp"
    >>> py_to_pg(float(0.5))
    "0.5::numeric"
    >>> py_to_pg(5)
    "5::int"
    >>> py_to_pg(['a','b','c'])
    "'{a,b,c}'::text[]"
    >>> py_to_pg(None)
    "'NULL'"
    >>> py_to_pg(33.00)
    "'33.0000'::numeric(5,4)"
    >>> py_to_pg(True)
    "'T'"
'''
def py_to_pg(pyval):
    # set precision to 4 decimals out
    getcontext().prec = 4
    t2t = {int: "'%s'::int",
        str: "'%s'::text",
        Decimal: '%s::numeric(5,4)',
        float: '%s::numeric(5,4)'}
    if type(pyval) in t2t:
        return t2t[type(pyval)] % (str(pyval),)
    elif type(pyval) == datetime.datetime:
        return "'%s'::timestamp" % (pyval.isoformat(),)
    elif type(pyval) == list:
        if len(pyval) > 0 and type(pyval[0]) in t2t:
            # grab appropriate type
            beginning = "'{"
            for a in pyval:
                beginning += str(a) + ','
            return beginning[0:-1] + "}'::" + re.sub(r'.+::(.+)',r'\1[]',t2t[type(pyval[0])])
        elif type(pyval[0]) == datetime.datetime:
            converted = [a.isoformat() for a in pyval]
            return re.sub(r'\[([^\]]+)\]',r"'{\1}'::timestamp[]", converted)
        elif not type(pyval[0]) in t2t:
            raise TypeError('py_to_pg not yet supports ARRAY type %s' % (str(type(pyval[0])),))
        else: # return an empty array
            return '{}'
    elif type(pyval) == type(None):
        return 'NULL'
    elif type(pyval) == bool:
        return "'%s'" % (str(pyval)[0],)
    else:
        raise TypeError('py_to_pg not yet supports type ' + str(type(pyval)))

和测试用例...

def test_py_to_pg(self):
    assertEquals(py_to_pg([decimal.Decimal(0.3),decimal.Decimal(0.3),decimal.Decimal(0.4)]), "'{0.299999999999999988897769753748434595763683319091796875,0.299999999999999988897769753748434595763683319091796875,0.40000000000000002220446049250313080847263336181640625}'::numeric(5,4)[]")
    assertEquals(py_to_pg([1,2,3]), "'{1,2,3}'::int[]")
    assertEquals(py_to_pg('Jack Johnson'), "'Jack Johnson'::text")
    assertEquals(py_to_pg([decimal.Decimal(0.3),decimal.Decimal(0.3),decimal.Decimal(0.4)]), "'{0.299999999999999988897769753748434595763683319091796875,0.299999999999999988897769753748434595763683319091796875,0.40000000000000002220446049250313080847263336181640625}'::numeric(5,4)[]")
    assertEquals(py_to_pg(decimal.Decimal(0.3)), '0.299999999999999988897769753748434595763683319091796875::numeric(5,4)')
    assertEquals(py_to_pg(datetime.datetime(2013,7,7,13,0,0)), "'2013-07-07T13:00:00'::timestamp")
    assertEquals(py_to_pg(float(0.5)), '0.5::numeric(5,4)')
    assertEquals(py_to_pg(0.5),'0.5::numeric(5,4)')
    assertEquals(py_to_pg(5), "'5'::int")
    assertEquals(py_to_pg(['a','b','c']), "'{a,b,c}'::text[]")
    assertEquals(py_to_pg(None), 'NULL')