Mystical comma in a Python expression -


this question has answer here:

i wondering comma in code:

line, =

the following example shows behavior:

import numpy np import matplotlib.pyplot plt   fig = plt.figure() ax = plt.axes(xlim=(0, 2), ylim=(-2, 2)) line, = ax.plot([], [], lw=2) print("first:") print(line) print("second:") line = ax.plot([], [], lw=2) print(line)

result:

first: line2d(_line0) second: [<matplotlib.lines.line2d object @ 0xb137c4c>]

it becomes confusing when try use line variable, , don't know whether use trailing comma or not:

def init():     line.set_data([], [])     return line,

or there better way avoids comma?

it's unpacking 1-tuple. eg:

line, = ('foo',)   # same line = 'foo' in example

compare with

line1, line2 = ('foo', 'bar') # unpack 2-tuple

etc.


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