Question

If we evaluate these lines one-by-one, x will be created in the context cc.

Begin["cc`"];
x = 1;
End[]

However, if we evaluate them together,

(Begin["cc`"];
x = 1;
End[])

then x will be created in Global. This is despite the following printing cc`:

(Begin["cc`"];
Print[$Context];
End[])

What is the reason for this behaviour? My guess is that contexts only matter during the parsing phase, not evaluation.

Use case: I wanted to create a palette Button that will define some symbols if they don’t exist yet, in a “private” context to avoid conflict with globals. What is the preferred method to do this, other than putting all the definitions in a package file and loading them from the palette? (I’d like to keep the palette self-contained.)

Answer 1

Symbols (and their contexts) are created when parsing, not evaluation. If we use $NewSymbol we can see this in effect:

$NewSymbol=Print["Name: ",#1," Context: ",#2]&;

Print["first"];
test1;
Print["last"]

(Print["first"];
 test2;
 Print["last"])

The first one prints:

first
Name: test1 Context: Global`
last

because each line in the cell is treated as a separate input. The second one uses parentheses to force all three lines to be considered one input and prints

Name: test2 Context: Global`
first
last

from which we can see that test2 was created in the Global` context before any evaluation occurred.

I think the easiest way to work with this is to use an explicit context on your symbol: cc`x = 1.