thomasbruggink opened a new pull request, #3753:
URL: https://github.com/apache/thrift/pull/3753
<!-- Explain the changes in the pull request below: -->
Fix the bug where the following:
```
struct C {
1: i32 value
}
struct A {
1: C nested = {}
}
struct B {
1: A itm = {}
}
```
would generate the following invalid python code:
```
class C:
thrift_spec = None
def __init__(self, value=None):
self.value = value
class A:
thrift_spec = None
def __init__(self, nested=C()):
if nested is self.thrift_spec[1][4]:
nested = C()
self.nested = nested
class B:
thrift_spec = None
def __init__(self, itm=A()):
if itm is self.thrift_spec[1][4]:
itm = A()
self.itm = itm
```
The problem with the above code is that `self.thrift_spec` was initialized
and set after the module was loaded. In python this would work when B is
instantiated but since B immediately invokes A() it happens before the
thrift_spec is set and this would result in `TypeError: 'NoneType' object is
not subscriptable`. By first initializing a temporary placeholder with a unique
address to compare to called `_THRIFT_DEFAULT` the generated code would look
like:
```
_THRIFT_DEFAULT = object()
class C:
def __init__(self, value=None):
self.value = value
class A:
def __init__(self, nested=_THRIFT_DEFAULT):
if nested is _THRIFT_DEFAULT:
nested = C()
class B:
def __init__(self, itm=_THRIFT_DEFAULT):
if itm is _THRIFT_DEFAULT:
itm = A()
```
Here the instantiation of the default object is defered until after the
module has been fully loaded resulting in the correct value being assigned.
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