Python 听写理解会产生看似不必要的错误
我正在使用Python 听写理解会产生看似不必要的错误,python,scope,list-comprehension,python-internals,dictionary-comprehension,Python,Scope,List Comprehension,Python Internals,Dictionary Comprehension,我正在使用brian2来运行神经网络模拟。为了在每次模拟期间记录数据,我创建了几个brian2的SpikeMonitor类的实例。我想将这些监视器存储在一个dict中,使用dict创建 作为测试,我在交互式会话中执行以下操作: In [1]: import brian2 In [2]: pe_mt = brian2.PoissonGroup(1, 100 * brian2.Hz) In [3]: record_pops = ['pe_mt'] In [4]: {'mon_' + pop:
brian2
来运行神经网络模拟。为了在每次模拟期间记录数据,我创建了几个brian2
的SpikeMonitor
类的实例。我想将这些监视器存储在一个dict中,使用dict创建
作为测试,我在交互式会话中执行以下操作:
In [1]: import brian2
In [2]: pe_mt = brian2.PoissonGroup(1, 100 * brian2.Hz)
In [3]: record_pops = ['pe_mt']
In [4]: {'mon_' + pop: brian2.SpikeMonitor(eval(pop)) for pop in record_pops}
Out[4]: {'mon_pe_mt': <SpikeMonitor, recording spikemonitor>}
并调用它,我得到以下错误
In [9]: tests.test_record()
---------------------------------------------------------------------------
NameError Traceback (most recent call last)
<ipython-input-9-4d3d585b2c97> in <module>()
----> 1 tests.test_record()
/home/daniel/Science/dopa_net/brian/ardid/tests.py in test_record()
61 record_pops = ['pe_mt']
62 return {'mon_' + pop: brian2.SpikeMonitor(eval(pop)) for pop in
---> 63 record_pops}
64 # DEBUG ###################
65 #monitors = utils.record(['pe_mt'], 'spikes', None, None, pe_mt, None, None)
/home/daniel/Science/dopa_net/brian/ardid/tests.py in <dictcomp>((pop,))
60 # DEBUG ###################
61 record_pops = ['pe_mt']
---> 62 return {'mon_' + pop: brian2.SpikeMonitor(eval(pop)) for pop in
63 record_pops}
64 # DEBUG ###################
/home/daniel/Science/dopa_net/brian/ardid/tests.py in <module>()
NameError: name 'pe_mt' is not defined
没有出现错误!我得到一个适当定义的SpikeMonitor
对象列表
一个已经被删除的答案建议我使用locals()[pop]
而不是eval(pop)
。请注意,这会引发一个等效错误:
In [20]: tests.test_record()
---------------------------------------------------------------------------
KeyError Traceback (most recent call last)
<ipython-input-20-4d3d585b2c97> in <module>()
----> 1 tests.test_record()
/home/daniel/Science/dopa_net/brian/ardid/tests.py in test_record()
61 record_pops = ['pe_mt']
62 return {'mon_' + pop: brian2.SpikeMonitor(locals()[pop]) for pop in
---> 63 record_pops}
64 # DEBUG ###################
65 #monitors = utils.record(['pe_mt'], 'spikes', None, None, pe_mt, None, None)
/home/daniel/Science/dopa_net/brian/ardid/tests.py in <dictcomp>((pop,))
60 # DEBUG ###################
61 record_pops = ['pe_mt']
---> 62 return {'mon_' + pop: brian2.SpikeMonitor(locals()[pop]) for pop in
63 record_pops}
64 # DEBUG ###################
KeyError: 'pe_mt'
[20]中的tests.test\u记录()
---------------------------------------------------------------------------
KeyError回溯(最近一次呼叫最后一次)
在()
---->1测试。测试记录()
/测试记录()中的home/daniel/Science/dopa_net/brian/ardid/tests.py
61记录_pops=['pe_mt']
62返回{'mon_'+pop:brian2.SpikeMonitor(locals()[pop]),用于pop-in
--->63记录_pops}
64#调试###################
65#监视器=utils.record(['pe#mt','spikes',None,None,pe#mt,None,None)
/home/daniel/Science/dopa_net/brian/ardid/tests.py in((pop,))
60#调试###################
61记录_pops=['pe_mt']
--->62返回{'mon_'+pop:brian2.SpikeMonitor(locals()[pop]),用于pop-in
63记录_pops}
64#调试###################
KeyError:“pe_mt”
一:忘记eval
,因为如果传递给它的字符串是表达式或函数调用,而不是标识符,那么它可能会导致意外情况发生。如果确实需要按名称获取局部变量,可以使用locals()[name]
干净地获取
文件:
第二:所有理解和生成器表达式(Python2.x中的列表理解除外),因此理解中的
locals()
将引用该表达式,即没有变量的表达式。这同样适用于eval
,即:
如果省略了局部字典,则默认为全局字典。如果省略了这两个字典,则表达式将在调用eval()的环境中执行
您可以通过提前获得它们来解决这一问题:
def test_record():
pe_mt = brian2.PoissonGroup(1, 100 * brian2.Hz)
record_pops = ['pe_mt']
groups = locals()
return {'mon_' + pop: brian2.SpikeMonitor(eval(pop, globals(), groups)) for pop in record_pops}
# or better
return {'mon_' + pop: brian2.SpikeMonitor(groups[pop]) for pop in record_pops}
或者更常规地,没有局部变量
:
def test_record():
groups = {
"pe_mt": brian2.PoissonGroup(1, 100 * brian2.Hz),
}
return {'mon_' + key: brian2.SpikeMonitor(value) for key, value in groups.iteritems()}
不推荐的解决方法:
def test_record():
pe_mt = brian2.PoissonGroup(1, 100 * brian2.Hz)
record_pops = ['pe_mt']
my_loc = locals()
return {'mon_' + pop: brian2.SpikeMonitor(eval(my_loc[pop])) for pop in
record_pops}
或者使用普通循环来构建dict:
def test_record():
pe_mt = brian2.PoissonGroup(1, 100 * brian2.Hz)
record_pops = ['pe_mt']
d = {}
for pop in record_pops:
d['mon_' + pop] = brian2.SpikeMonitor(locals()[pop]))
return d
或者简单地使用dict来保存对象:
def test_record():
d = {"pe_mt":brian2.PoissonGroup(1, 100 * brian2.Hz)}
record_pops = ['pe_mt']
return {'mon_' + pop: brian2.SpikeMonitor(d[pop]) for pop in record_pops}
eval(pop)
应该做什么?在这里,pop='peu mt.
eval(pop)
给了我一个peu mt
对象,一个SpikeMonitor
。为什么不直接存储这个对象呢?我很困惑。存储对象正是我想做的。你的问题是dict理解有它自己的局部作用域。你能证明locals()。此外,在这里,您必须事先构造局部变量
,因此调用eval
从该字典中获取一个值是非常迂回的,因为它会阻止编译器优化您的代码。您有什么建议?那么这段代码会阻止优化吗?是否有人必须使用eval?如果最后一个代码块的实用程序只在必须使用eval的情况下才使用,那么包含它似乎很愚蠢。@dbliss,您是否手动创建了所有对象?我看不出你的代码在结构上有什么优势。您可以直接存储对象基本上return{'mon_uu'+str(ind):brian2.SpikeMonitor(pop)for ind,pop in enumerate(record_pops)}
或者如果您想保留一个全局计数器,它将在对象添加到dict时递增,请使用itertools.count()
在代码开头声明它
def test_record():
pe_mt = brian2.PoissonGroup(1, 100 * brian2.Hz)
record_pops = ['pe_mt']
d = {}
for pop in record_pops:
d['mon_' + pop] = brian2.SpikeMonitor(locals()[pop]))
return d
def test_record():
d = {"pe_mt":brian2.PoissonGroup(1, 100 * brian2.Hz)}
record_pops = ['pe_mt']
return {'mon_' + pop: brian2.SpikeMonitor(d[pop]) for pop in record_pops}