1

我brian2用来运行神经网络模拟。为了在每次模拟期间记录数据，我正在创建brian2'sSpikeMonitor类的几个实例化。我想将这些监视器存储在使用字典理解创建的字典中。

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>}

一切看起来都很棒。但是现在当我将此代码移动到以下函数中时

def test_record():
    pe_mt = brian2.PoissonGroup(1, 100 * brian2.Hz)
    record_pops = ['pe_mt']
    return {'mon_' + pop: brian2.SpikeMonitor(eval(pop)) for pop in
            record_pops}

并调用它，我收到以下错误

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

这里发生了什么？'pe_mt'在函数中定义。

请注意，如果我将 dict 理解更改为列表理解，如

return [brian2.SpikeMonitor(eval(pop)) for pop in record_pops]

没有错误被提出！我得到了一个SpikeMonitor适当定义的对象列表。

现在已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'
4

2 回答 2

0

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，它可能会导致意外的事情发生。如果您确实需要按名称获取局部变量，您可以使用locals()[name].

文件：locals

二：所有推导和生成器表达式（python 2.x 中的列表推导除外）都有自己的 namespace，因此locals()推导内部将引用那个 - 没有你的变量的那个。eval默认情况下捕获您的局部变量也是如此：

如果 locals 字典被省略，则默认为 globals 字典。如果省略了两个字典，则表达式将在调用 eval() 的环境中执行。

您可以通过更早地获取它们来解决这个问题：

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}

或者更传统地说，没有locals：

def test_record():
    groups = {
        "pe_mt": brian2.PoissonGroup(1, 100 * brian2.Hz),
    }
    return {'mon_' + key: brian2.SpikeMonitor(value) for key, value in groups.iteritems()}
于 2015-04-09T19:50:22.703 回答
0

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}

或者使用一个普通的循环来构建你的字典：

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}
于 2015-04-09T20:06:53.177 回答