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Date: Thu, 14 May 2015 13:06:09 -0500
Subject: a python pitfall
From: Billy Earney <billy.earney@gmail.com>
To: "python-list@python.org" <python-list@python.org>
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Hello friends:

I saw the following example at
http://nafiulis.me/potential-pythonic-pitfalls.html#using-mutable-default-arguments
and
did not believe the output produced and had to try it for myself....

def foo(a,b,c=[]):
    c.append(a)
    c.append(b)
    print(c)

foo(1,1)
foo(1,1)
foo(1,1)

produces:
[1, 1]
[1, 1, 1, 1]
[1, 1, 1, 1, 1, 1]

One would expect the following output:
[1, 1]
[1, 1]
[1, 1]

Doesn't this valid the zen of python: "Explicit is better than implicit."  ?

Thanks!
Billy

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<div dir=3D"ltr"><div>Hello friends:</div><div><br></div>I saw the followin=
g example at=C2=A0<a href=3D"http://nafiulis.me/potential-pythonic-pitfalls=
.html#using-mutable-default-arguments">http://nafiulis.me/potential-pythoni=
c-pitfalls.html#using-mutable-default-arguments</a>=C2=A0and did not believ=
e the output produced and had to try it for myself....<div><br></div><div><=
div>def foo(a,b,c=3D[]):</div><div>=C2=A0 =C2=A0 c.append(a)</div><div>=C2=
=A0 =C2=A0 c.append(b)</div><div>=C2=A0 =C2=A0 print(c)</div><div><br></div=
><div>foo(1,1)</div><div>foo(1,1)</div><div>foo(1,1)</div><div><br></div><d=
iv>produces:</div><div><div>[1, 1]</div><div>[1, 1, 1, 1]</div><div>[1, 1, =
1, 1, 1, 1]</div></div><div><br></div><div>One would expect the following o=
utput:<br></div></div><div>[1, 1]</div><div>[1, 1]</div><div>[1, 1]</div><d=
iv><br></div><div>Doesn&#39;t this valid the zen of python: &quot;Explicit =
is better than implicit.&quot; =C2=A0?</div><div><br></div><div>Thanks!</di=
v><div>Billy</div></div>

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