行,= plot(x,sin(x))逗号代表什么? [英] line, = plot(x,sin(x)) what does comma stand for?
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问题描述
我正在尝试制作动画情节.这是示例代码:
I'm trying to make an animated plot. Here is an example code:
from pylab import *
import time
ion()
tstart = time.time() # for profiling
x = arange(0,2*pi,0.01) # x-array
line, = plot(x,sin(x))
for i in arange(1,200):
line.set_ydata(sin(x+i/10.0)) # update the data
draw() # redraw the canvas
print 'FPS:' , 200/(time.time()-tstart)
我不了解line,
.没有逗号,代码将无法正常工作.
I don't understand the line,
. Without comma, the code doesn't work.
推荐答案
逗号是Python语法,表示单元素元组.例如,
The comma is Python syntax that denotes either a single-element tuple. E.g.,
>>> tuple([1])
(1,)
在这种情况下,它用于参数解压:plot
返回一个单元素列表,该列表被解压到line
:
In this case, it is used for argument unpacking: plot
returns a single-element list, which is unpacked into line
:
>>> x, y = [1, 2]
>>> x
1
>>> y
2
>>> z, = [3]
>>> z
3
另一种可能更易读的方法是使用类似列表的语法:
An alternative, perhaps more readable way of doing this is to use list-like syntax:
>>> [z] = [4]
>>> z
4
尽管z, =
在Python代码中更常见.
though the z, =
is more common in Python code.
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