Globals not set by default for eval() when embedding

[gelldur]

Issue description

Example from documentation isn't working
http://pybind11.readthedocs.io/en/master/advanced/embedding.html#getting-started

 py::exec(R"(
 kwargs = dict(name="World", number=42)
 message = "Hello, {name}! The answer is {number}".format(**kwargs)
 print(message)
 )");

Error:

terminate called after throwing an instance of 'pybind11::error_already_set'
 what(): NameError: name 'dict' is not defined

At:
 <string>(3): <module>

This also isn't working:

	py::exec(R"(
 #kwargs = {'name':"World", 'number':42}
 #message = "Hello, {name}! The answer is {number}".format(**kwargs)
 print("Hello")
 )");

Error:

terminate called after throwing an instance of 'pybind11::error_already_set'
 what(): NameError: name 'print' is not defined

At:
 <string>(5): <module>

Reproducible example code

#include <iostream>

#include <pybind11/embed.h> // everything needed for embedding

namespace py = pybind11;

int main()
{
	py::scoped_interpreter guard{}; // start the interpreter and keep it alive

	py::exec(R"(
 kwargs = dict(name="World", number=42)
 message = "Hello, {name}! The answer is {number}".format(**kwargs)
 print(message)
 )");

	py::exec(R"(
 #kwargs = {'name':"World", 'number':42}
 #message = "Hello, {name}! The answer is {number}".format(**kwargs)
 print("Hello")
 )");
	return 0;
}

[gelldur]

@jagerman so bug in documentation yeah ? but what about print ?

[jagerman]

Edit: Err, never mind those weren't c++ calls (apologies--I was reading too quickly from my phone).

[jagerman]

The print is probably a matter of using Python 2 rather than 3.

[gelldur]

Even if i set python 3.6 in cmake still doesn't work :(

Checked even for python2

	py::exec(R"(
 #kwargs = {'name':"World", 'number':42}
 #message = "Hello, {name}! The answer is {number}".format(**kwargs)
 print "Hello"
 )");

terminate called after throwing an instance of 'pybind11::error_already_set'
 what(): SyntaxError: ('invalid syntax', ('<string>', 5, 13, 'print "Hello"\n'))

[jagerman]

Confirmed. Cc @dean0x7d: it seems as though when called for an embedded interpreter PyEval_GetGlobals returns NULL, because there is no current execution frame.

Adding py::globals to the example will fix it, but that feels to me like something that should be the default: perhaps in eval(), if globals is unset and PyEval_GetGlobals() returns NULL, we should fall back to py::globals() instead of an empty dict()?

[dean0x7d]

Resolved in #889. Thanks for reporting the issue @gelldur!