Why does variable suddenly get out of scope ? (python 3)

Question

still learning python.

In this code, I can reference v0 and v1 to compute v2 inside the Foo class. So far, so good.

class Foo():

  v0="abcd"
  v1="efgh"
  v2=(v0, v1)
  #v3=[(v0, c) for c in v2]     # NameError: name 'v0' is not defined.
  #v3=[("abcd", c) for c in v2] # Works

print(Foo.v0, Foo.v1, Foo.v2)
#print(Foo.v0, Foo.v1, Foo.v2, Foo.v3)

But if I uncomment the v3=[(v0, c) for c in v2] line, I get an error that states v0 is not defined.

Traceback (most recent call last):
  File "/private/tmp/machin.py", line 1, in <module>
    class Foo():
  File "/private/tmp/machin.py", line 6, in Foo
    v3=[(v0, c) for c in v2]
  File "/private/tmp/machin.py", line 6, in <listcomp>
    v3=[(v0, c) for c in v2]
NameError: name 'v0' is not defined. Did you mean: '.0'?

Strangely enough, v2 does not receive the same treatment and this line works :

    v3=[("abcd", c) for c in v2]

Reading the python doc about classes, scopes and namespaces does not help me to understand what is happening...

So questions :

1. Why is the variable v0 suddenly out of scope but v2 is still reachable ?
2. Is there a workaround that does not involve retyping the v0 literal again ? Which one ?