在python中，如果有多个连续的Try-Except子句，并且只有当所有这些子句都成功时才触发一个Else子句，该如何实现？例如，以下代码中，只有当所有Voltmeter都成功初始化时，才希望打印“仪表已初始化”。但是，目前代码只取决于加热器温度计。
try:
private.anodization_voltage_meter = Voltmeter(voltage_meter_address.value) #assign voltmeter location
except(visa.VisaIOError): #channel time out
private.logger.warning('Volt Meter is not on or not on this channel')
try:
private.anodization_current_meter = Voltmeter(current_meter_address.value) #assign voltmeter as current meter location
except(visa.VisaIOError): #channel time out
private.logger.warning('Ammeter is not on or not on this channel')
try:
private.sample_thermometer = Voltmeter(sample_thermometer_address.value)#assign voltmeter as thermomter location for sample.
except(visa.VisaIOError): #channel time out
private.logger.warning('Sample Thermometer is not on or not on this channel')
try:
private.heater_thermometer = Voltmeter(heater_thermometer_address.value)#assign voltmeter as thermomter location for heater.
except(visa.VisaIOError): #channel time out
private.logger.warning('Heater Thermometer is not on or not on this channel')
else:
private.logger.info('Meters initialized')
2、解决方案
以下是一些可能的解决方案：
解决方案1：使用函数和all()
一种方式是将try/except结构分解成一个函数，如果调用成功则返回True，如果调用失败则返回False，然后使用all()来查看它们是否都成功了。例如：
def initfunc(structure, attrname, address, desc):
try:
var = Voltmeter(address.value)
setattr(structure, attrname, var)
return True
except(visa.VisaIOError):
structure.logger.warning('%s is not on or not on this channel' % (desc,))
if all([initfunc(*x) for x in [(private, 'anodization_voltage_meter', voltage_meter_address, 'Volt Meter'), ...]]):
private.logger.info('Meters initialized')
解决方案2：使用trip变量
另一种方式是使用一个trip变量，如init_ok，将其设置为True，并在所有except子句中将其设置为False，最后再进行测试。例如：
init_ok = True
for meter, address, message in (
('anodization_voltage_meter',voltage_meter_address,'Volt Meter is not on or not on this channel'),
('anodization_current_meter',current_meter_address,'Ammeter is not on or not on this channel'),
('sample_thermometer',sample_thermometer_address,'Sample Thermometer is not on or not on this channel'),
('heater_thermometer',heater_thermometer_address,'Heater Thermometer is not on or not on this channel')):
try:
setattr(private,meter, Voltmeter(address.value):
except (visa.VisaIOError,):
init_ok = False
private.logger.warning(message)
if init_ok: # everything is ok
private.logger.info('Meters initialized')
解决方案3：使用布尔变量
还可以使用一个布尔变量，在开头初始化为True：everythingOK=True。然后在所有的except块中将其设置为False，只有在true的情况下才记录最后一行。例如：
success = True
for meter, address, message in (
('anodization_voltage_meter',voltage_meter_address,'Volt Meter is not on or not on this channel'),
('anodization_current_meter',current_meter_address,'Ammeter is not on or not on this channel'),
('sample_thermometer',sample_thermometer_address,'Sample Thermometer is not on or not on this channel'),
('heater_thermometer',heater_thermometer_address,'Heater Thermometer is not on or not on this channel')):
try:
setattr(private,meter, Voltmeter(address.value):
except (visa.VisaIOError,):
success = False
private.logger.warning(message)
if success: # everything is ok
private.logger.info('Meters initialized')
解决方案4：使用数据驱动的解决方案
如果有多个相似性对象，可以使用数据驱动的解决方案。例如，可以创建一个包含所有对象的类，并使用这个类来初始化所有的对象。这样可以简化代码并提高可读性。
class MeterConfiguration(object):
def __init__(self, name, address):
self.name = name
self.address = address
def english_name(self):
"""A readable form of the name for this meter."""
return ' '.join(x.title() for x in self.name.split('_')) + ' Meter'
ALL_METERS = [
MeterConfiguration('anodization_voltage', 'PORT0001'),
MeterConfiguration('anodization_current', 'PORT0002'),
MeterConfiguration('sample_thermometer', 'PORT0003'),
MeterConfiguration('heater_thermometer', 'PORT0004')
]
private.meters = {}
any_errors = False
for meter in ALL_METERS:
try:
private.meters[meter.name] = Voltmeter(meter.address)
except VisaError:
logging.error('%s not found at %s', meter.english_name(), meter.address)
any_errors = True
if not any_errors:
logging.info('All meters initialized.')
