我们从Python开源项目中，提取了以下11个代码示例，用于说明如何使用decimal.Context()。
def float_to_decimal(f): """ Convert a floating point number to a Decimal with no loss of information. Intended for Python 2.6 where casting float to Decimal does not work. """ n, d = f.as_integer_ratio() numerator, denominator = Decimal(n), Decimal(d) ctx = Context(prec=60) result = ctx.divide(numerator, denominator) while ctx.flags[Inexact]: ctx.flags[Inexact] = False ctx.prec *= 2 result = ctx.divide(numerator, denominator) return result
def round_py2_compat(what): """ Python 2 and Python 3 use different rounding strategies in round(). This function ensures that results are python2/3 compatible and backward compatible with previous py2 releases :param what: float :return: rounded long """ d = Context( prec=len(str(long(what))), # round to integer with max precision rounding=decimal.ROUND_HALF_UP ).create_decimal(str(what)) # str(): python 2.6 compat return long(d)
def float_to_decimal(f): """Convert a floating point number to a Decimal with no loss of information. See: http://docs.python.org/release/2.6.7/library/decimal.html#decimal-faq """ n, d = f.as_integer_ratio() numerator, denominator = Decimal(n), Decimal(d) ctx = Context(prec=60) result = ctx.divide(numerator, denominator) while ctx.flags[Inexact]: ctx.flags[Inexact] = False ctx.prec *= 2 result = ctx.divide(numerator, denominator) return result
def create_decimal128_context(): """Returns an instance of :class:`decimal.Context` appropriate for working with IEEE-754 128-bit decimal floating point values. """ opts = _CTX_OPTIONS.copy() opts['traps'] = [] return decimal.Context(**opts)
def _context_equal(x, y, ctx): """Return True if both objects are equal based on the provided context. Args: x (numeric): A numeric value. y (numeric): A numeric value. ctx (:class:`decimal.Context`): A decimal Context object. Returns: :obj:`bool`: True if the values are equal based on the provided context, False otherwise. """ if x is not None: if y is None: return False # Note: The float conversion is because these may come in as # numpy.float32 or numpy.float64, which Decimal does not know # how to handle. if (Decimal(float(x)).normalize(ctx) != Decimal(float(y)).normalize(ctx)): return False else: if y is not None: return False return True
def __eq__(self, other): """Return True if this projection object is the same as *other*. Note: WRF can use either floats or doubles, so only going to guarantee floating point precision equivalence, in case the different types are ever compared (or a projection is hand constructed). For WRF domains, 7-digit equivalence should be good enough. """ if self.map_proj is not None: if self.map_proj != other.map_proj: return False else: if other.map_proj is not None: return False # Only checking for floating point equal. ctx = Context(prec=7, rounding=ROUND_HALF_UP) return (WrfProj._context_equal(self.truelat1, other.truelat1, ctx) and WrfProj._context_equal(self.truelat2, other.truelat2, ctx) and WrfProj._context_equal(self.moad_cen_lat, other.moad_cen_lat, ctx) and WrfProj._context_equal(self.stand_lon, other.stand_lon, ctx) and WrfProj._context_equal(self.pole_lat, other.pole_lat, ctx) and WrfProj._context_equal(self.pole_lon, other.pole_lon, ctx) and WrfProj._context_equal(self.dx, other.dx, ctx) and WrfProj._context_equal(self.dy, other.dy, ctx))
def bench_telco(loops, filename): getcontext().rounding = ROUND_DOWN rates = list(map(Decimal, ('0.0013', '0.00894'))) twodig = Decimal('0.01') Banker = Context(rounding=ROUND_HALF_EVEN) basictax = Decimal("0.0675") disttax = Decimal("0.0341") with open(filename, "rb") as infil: data = infil.read() infil = io.BytesIO(data) outfil = six.StringIO() start = perf.perf_counter() for _ in range(loops): infil.seek(0) sumT = Decimal("0") # sum of total prices sumB = Decimal("0") # sum of basic tax sumD = Decimal("0") # sum of 'distance' tax for i in xrange(5000): datum = infil.read(8) if datum == '': break n, = unpack('>Q', datum) calltype = n & 1 r = rates[calltype] p = Banker.quantize(r * n, twodig) b = p * basictax b = b.quantize(twodig) sumB += b t = p + b if calltype: d = p * disttax d = d.quantize(twodig) sumD += d t += d sumT += t print(t, file=outfil) outfil.seek(0) outfil.truncate() return perf.perf_counter() - start
def pretty_description(self, show_positions=True, filename=None): if filename: pfx = filename.rstrip().rstrip(':') + ':' else: pfx = '' # Print file position as numeric abbreviation err = pfx if self.position == 0: err += '0:0:' elif self.position: err += '%d:%d:' % (self.position.line, self.position.column) else: err += ' ' # Print severity and main error message err += " %s: %s" % (self.severity.capitalize(), self.message) if len(self.args) > 1: err += ': ' for anum, a in enumerate(self.args[1:]): if anum > 1: err += ', ' astr = repr(a) if len(astr) > 30: astr = astr[:30] + '...' err += astr # Print out exception chain e2 = self while e2: if hasattr(e2,'__cause__') and isinstance(e2.__cause__,Exception): e2 = e2.__cause__ e2desc = str(e2).strip() if not e2desc: e2desc = repr(e2).strip() err += "\n | Cause: %s" % e2desc.strip().replace('\n','\n | ') else: e2 = None # Show file position if show_positions and self.position is not None: if self.position == 0: err += "\n | At start of input" else: err += "\n | At %s" % (self.position.describe(show_text=False),) if self.position.text_after: err += "\n | near text: %r" % (self.position.text_after,) # Show context if show_positions and self.outer_position: if self.context_description: cdesc = self.context_description.capitalize() else: cdesc = "Context" err += "\n | %s started at %s" % (cdesc, self.outer_position.describe(show_text=False),) if self.outer_position.text_after: err += "\n | with text: %r" % (self.outer_position.text_after,) return err
