add variable interpolation

Author: marius311

docs/source/usage.md

@@ -70,7 +70,7 @@ You can then use, e.g.,
 In IPython (and therefore in Jupyter), you can directly execute Julia
 code using `%%julia` magic:
 
-```
+```none
 In [1]: %load_ext julia.magic
 Initializing Julia interpreter. This may take some time...
 
@@ -86,6 +86,35 @@ In [2]: %%julia
 |__/                   |
 ```
 
+Any `$var` or `$(var)` expressions that appear in the Julia code (except in
+comments or string literals) are evaluated in Python and passed to Julia. Use
+`$$var` to insert a literal `$var` in Julia code.
+
+```none
+In [3]: foo = [[1,2],[3,4]]
+
+In [4]: %julia $foo .+ 1
+
+Out[4]: 
+array([[2, 3],
+       [4, 5]], dtype=int64)
+       
+In [22]: %%julia
+   ...: bar=3
+   ...: :($$bar)
+   
+Out[22]: 3
+
+```
+
+Variables are automatically converted between equivalent Python/Julia types (should they exist) using PyCall. Note below that `1`, `x`, and the tuple itself are converted to Julia `Int64`, `String`, and `Tuple`, respectively, although the function `abs` and the result of `typeof` are not.
+
+```none
+In [6]: %julia typeof($(1,"x",abs))
+
+Out[6]: <PyCall.jlwrap Tuple{Int64,String,PyObject}>
+```
+
 #### IPython configuration
 
 PyJulia-IPython integration can be configured via IPython's

src/julia/magic.py

@@ -22,7 +22,7 @@
 import sys
 import warnings
 
-from IPython.core.magic import Magics, magics_class, line_cell_magic
+from IPython.core.magic import Magics, magics_class, line_cell_magic, no_var_expand
 from IPython.utils import py3compat as compat
 from traitlets import Bool, Enum
 
@@ -89,6 +89,7 @@ def __init__(self, shell):
         self._julia = Julia(init_julia=True)
         print()
 
+    @no_var_expand
     @line_cell_magic
     def julia(self, line, cell=None):
         """
@@ -97,14 +98,9 @@ def julia(self, line, cell=None):
         """
         src = compat.unicode_type(line if cell is None else cell)
 
-        try:
-            ans = self._julia.eval(src)
-        except JuliaError as e:
-            print(e, file=sys.stderr)
-            ans = None
-
-        return ans
-
+        return self._julia.eval("""
+        _PyJuliaHelper.@prepare_for_pyjulia_call begin %s end
+        """%src)(self.shell.user_ns, self.shell.user_ns)
 
 # Add to the global docstring the class information.
 __doc__ = __doc__.format(

src/julia/pyjulia_helper.jl

@@ -1,5 +1,10 @@
 module _PyJuliaHelper
 
+using PyCall
+using PyCall: pyeval_
+using MacroTools
+using MacroTools: isexpr
+
 if VERSION < v"0.7-"
 nameof(m::Module) = ccall(:jl_module_name, Ref{Symbol}, (Any,), m)
 
@@ -44,6 +49,33 @@ if VERSION >= v"0.7-"
     end
 end
 
+
+macro prepare_for_pyjulia_call(ex)
+    
+    # f(x) returns transformed expression x and whether to recurse 
+    # into the new expression
+    function walk(f, x)
+        (fx, recurse) = f(x)
+        MacroTools.walk(fx, (recurse ? (x -> walk(f,x)) : identity), identity)
+    end
+    
+    ex = walk(ex) do x
+        if isexpr(x, :$)
+            if isexpr(x.args[1], :$)
+                x.args[1], false
+            else
+                :($convert($PyAny, $pyeval_($("$(x.args[1])"),__globals,__locals))), true
+            end
+        else
+            x, true
+        end 
+    end
+    esc(quote
+        $pyfunction((__globals,__locals) -> $ex, $PyObject, $PyObject)
+    end)
+end
+
+
 module IOPiper
 
 const orig_stdin  = Ref{IO}()