[英]Why timeit doesn't work on my code snippet?
我認為這三個在邏輯上是等價的,返回集合{1, 3, 4}
:
set(sum(((1, 3), (4,), (1,)), ()))
set(sum([[1, 3], [4], [1]], []))
functools.reduce(operator.or_, ({1, 3}, {4}, {1}), set())
但是當我嘗試在ipython(python 3.4.0上的v1.2.1)中檢查每個的性能時,timeit magic失敗了。
In [1]: from operator import or_; from functools import reduce
In [2]: timeit set(sum([[1, 3], [4], [1]], []))
1000000 loops, best of 3: 604 ns per loop
In [3]: timeit set(sum(((1, 3), (4,), (1,)), ()))
1000000 loops, best of 3: 330 ns per loop
In [4]: timeit reduce(or_, ({1, 3}, {4}, {1}), set())
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-4-83628f6293f3> in <module>()
----> 1 get_ipython().magic('timeit reduce(or_, ({1, 3}, {4}, {1}), set())')
/usr/lib/python3/dist-packages/IPython/core/interactiveshell.py in magic(self, arg_s)
2164 magic_name, _, magic_arg_s = arg_s.partition(' ')
2165 magic_name = magic_name.lstrip(prefilter.ESC_MAGIC)
-> 2166 return self.run_line_magic(magic_name, magic_arg_s)
2167
2168 #-------------------------------------------------------------------------
/usr/lib/python3/dist-packages/IPython/core/interactiveshell.py in run_line_magic(self, magic_name, line)
2085 kwargs['local_ns'] = sys._getframe(stack_depth).f_locals
2086 with self.builtin_trap:
-> 2087 result = fn(*args,**kwargs)
2088 return result
2089
/usr/lib/python3/dist-packages/IPython/core/magics/execution.py in timeit(self, line, cell)
/usr/lib/python3/dist-packages/IPython/core/magic.py in <lambda>(f, *a, **k)
190 # but it's overkill for just that one bit of state.
191 def magic_deco(arg):
--> 192 call = lambda f, *a, **k: f(*a, **k)
193
194 if isinstance(arg, collections.Callable):
/usr/lib/python3/dist-packages/IPython/core/magics/execution.py in timeit(self, line, cell)
929 number = 1
930 for i in range(1, 10):
--> 931 if timer.timeit(number) >= 0.2:
932 break
933 number *= 10
/usr/lib/python3.4/timeit.py in timeit(self, number)
176 gc.disable()
177 try:
--> 178 timing = self.inner(it, self.timer)
179 finally:
180 if gcold:
<magic-timeit> in inner(_it, _timer)
TypeError: unsupported operand type(s) for |: 'set' and 'tuple'
這里發生了什么? 在2.7中也失敗了。 我無法使用vanilla python timeit.timeit
方法重現這一點。
這在我看來是IPython中的一個錯誤。
逃避大括號,以便通話看起來像
timeit reduce(or_, ({{1, 3}}, {{4}}, {{1}}), set())
如果你看到調用堆棧,在調用級聯到timeit.py之前,它會通過
/usr/lib/python3/dist-packages/IPython/core/interactiveshell.py in run_line_magic(self, magic_name, line)
2085 kwargs['local_ns'] = sys._getframe(stack_depth).f_locals
2086 with self.builtin_trap:
-> 2087 result = fn(*args,**kwargs)
2088 return result
現在,如果您引用此源代碼,您可以看到,在將參數傳遞給timeit
函數之前,將其格式化為在字符串中展開Python變量
magic_arg_s = self.var_expand(line, stack_depth)
# Put magic args in a list so we can call with f(*a) syntax
args = [magic_arg_s]
self.var_expand
將DollarFormatter()
調用為for-matter函數,其doc-string表示以下行中的內容
class DollarFormatter(FullEvalFormatter):
"""Formatter allowing Itpl style $foo replacement, for names and attribute
access only. Standard {foo} replacement also works, and allows full
evaluation of its arguments.
所以,這就是原因,一個集合被解釋為標准的{foo}替換並轉換為元組(如果用逗號分隔的值)或一個使表達式為
reduce(or_, ((1, 3), 4, 1), set())
這是偏離無效的。
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