You can't do that in Python.
What you can do instead is store the results under a dictionary with key = England_M
for instance.
In your case, you could do the following :
def func(dataFrame,country,sex):
tmp = dataFrame[(dataFrame['land']==country) & (dataFrame['sex']==sex)]
variable_name = "{c}_{s}".format(c=country, s=sex)
return dict(variable_name=tmp)
Now using it :
results = func(dataFrame, "England", "M")
print(results['England_M'])