iPython: 为什么在 运行 with %%timeit 时 for 循环会抛出异常
iPython: why does for loop throw an exception when run with %%timeit
我正在尝试在 iPython 中进行一些分析，但我无法理解为什么下面的 for 循环在使用 %%timeit.
执行时会抛出异常
没有任何分析，循环工作正常。为什么循环在分析时抛出异常 and/or 如何修改循环使其不抛出异常？
In [1]: import numpy as np
...: import pandas as pd
In [2]: df = pd.DataFrame([[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16]])
In [3]: df.columns = pd.MultiIndex.from_tuples(
...: (("df1", "d"), ("df1", "g"), ("df2", "d"), ("df2", "g"))
...: )
In [4]: df
Out[4]:
df1 df2
d g d g
0 1 2 3 4
1 5 6 7 8
2 9 10 11 12
3 13 14 15 16
In [5]: df1 = df.copy()
In [6]: for c in df.columns.levels[0]:
...: d = df.stack().droplevel(0).loc["d", c]
...: df[c, "lr"] = np.log(d.values / d.shift().values)
...: df = df.sort_index(axis=1)
In [7]: df
Out[7]:
df1 df2
d g lr d g lr
0 1 2 NaN 3 4 NaN
1 5 6 1.609438 7 8 0.847298
2 9 10 0.587787 11 12 0.451985
3 13 14 0.367725 15 16 0.310155
In [8]: %%timeit
...: for c in df1.columns.levels[0]:
...: d = df1.stack().droplevel(0).loc["d", c]
...: df1[c, "lr"] = np.log(d.values / d.shift().values)
...: df1 = df1.sort_index(axis=1)
UnboundLocalError: local variable 'df1' referenced before assignment
我的会话中有一个数组：
In [80]: arr
Out[80]:
array([ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,
17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29])
In [81]: %%timeit
...: arr = arr.copy()
...:
...:
Traceback (most recent call last):
File "<ipython-input-81-9a73362a3bde>", line 1, in <module>
get_ipython().run_cell_magic('timeit', '', 'arr = arr.copy()\n\n')
File "/usr/local/lib/python3.8/dist-packages/IPython/core/interactiveshell.py", line 2419, in run_cell_magic
result = fn(*args, **kwargs)
File "<decorator-gen-53>", line 2, in timeit
File "/usr/local/lib/python3.8/dist-packages/IPython/core/magic.py", line 187, in <lambda>
call = lambda f, *a, **k: f(*a, **k)
File "/usr/local/lib/python3.8/dist-packages/IPython/core/magics/execution.py", line 1180, in timeit
time_number = timer.timeit(number)
File "/usr/local/lib/python3.8/dist-packages/IPython/core/magics/execution.py", line 169, in timeit
timing = self.inner(it, self.timer)
File "<magic-timeit>", line 1, in inner
UnboundLocalError: local variable 'arr' referenced before assignment
但分配给不同的名称是可以的：
In [82]: %%timeit
...: arr1 = arr.copy()
...:
...:
...:
486 ns ± 14.3 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
我们在函数定义中遇到同样的错误：
In [84]: def foo():
...: arr1 = arr.copy()
...:
In [85]: foo()
In [86]: def foo():
...: arr = arr.copy()
...:
In [87]:
In [87]: foo()
Traceback (most recent call last):
File "<ipython-input-87-c19b6d9633cf>", line 1, in <module>
foo()
File "<ipython-input-86-f6fd187c7954>", line 2, in foo
arr = arr.copy()
UnboundLocalError: local variable 'arr' referenced before assignment
timeit将代码包装在一个函数中，然后多次执行。
我正在尝试在 iPython 中进行一些分析，但我无法理解为什么下面的 for 循环在使用 %%timeit.
没有任何分析，循环工作正常。为什么循环在分析时抛出异常 and/or 如何修改循环使其不抛出异常？
In [1]: import numpy as np
...: import pandas as pd
In [2]: df = pd.DataFrame([[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16]])
In [3]: df.columns = pd.MultiIndex.from_tuples(
...: (("df1", "d"), ("df1", "g"), ("df2", "d"), ("df2", "g"))
...: )
In [4]: df
Out[4]:
df1 df2
d g d g
0 1 2 3 4
1 5 6 7 8
2 9 10 11 12
3 13 14 15 16
In [5]: df1 = df.copy()
In [6]: for c in df.columns.levels[0]:
...: d = df.stack().droplevel(0).loc["d", c]
...: df[c, "lr"] = np.log(d.values / d.shift().values)
...: df = df.sort_index(axis=1)
In [7]: df
Out[7]:
df1 df2
d g lr d g lr
0 1 2 NaN 3 4 NaN
1 5 6 1.609438 7 8 0.847298
2 9 10 0.587787 11 12 0.451985
3 13 14 0.367725 15 16 0.310155
In [8]: %%timeit
...: for c in df1.columns.levels[0]:
...: d = df1.stack().droplevel(0).loc["d", c]
...: df1[c, "lr"] = np.log(d.values / d.shift().values)
...: df1 = df1.sort_index(axis=1)
UnboundLocalError: local variable 'df1' referenced before assignment
我的会话中有一个数组：
In [80]: arr
Out[80]:
array([ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,
17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29])
In [81]: %%timeit
...: arr = arr.copy()
...:
...:
Traceback (most recent call last):
File "<ipython-input-81-9a73362a3bde>", line 1, in <module>
get_ipython().run_cell_magic('timeit', '', 'arr = arr.copy()\n\n')
File "/usr/local/lib/python3.8/dist-packages/IPython/core/interactiveshell.py", line 2419, in run_cell_magic
result = fn(*args, **kwargs)
File "<decorator-gen-53>", line 2, in timeit
File "/usr/local/lib/python3.8/dist-packages/IPython/core/magic.py", line 187, in <lambda>
call = lambda f, *a, **k: f(*a, **k)
File "/usr/local/lib/python3.8/dist-packages/IPython/core/magics/execution.py", line 1180, in timeit
time_number = timer.timeit(number)
File "/usr/local/lib/python3.8/dist-packages/IPython/core/magics/execution.py", line 169, in timeit
timing = self.inner(it, self.timer)
File "<magic-timeit>", line 1, in inner
UnboundLocalError: local variable 'arr' referenced before assignment
但分配给不同的名称是可以的：
In [82]: %%timeit
...: arr1 = arr.copy()
...:
...:
...:
486 ns ± 14.3 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
我们在函数定义中遇到同样的错误：
In [84]: def foo():
...: arr1 = arr.copy()
...:
In [85]: foo()
In [86]: def foo():
...: arr = arr.copy()
...:
In [87]:
In [87]: foo()
Traceback (most recent call last):
File "<ipython-input-87-c19b6d9633cf>", line 1, in <module>
foo()
File "<ipython-input-86-f6fd187c7954>", line 2, in foo
arr = arr.copy()
UnboundLocalError: local variable 'arr' referenced before assignment
timeit将代码包装在一个函数中，然后多次执行。