Implement a pyimport string macro

This helps usability by automatically converting Python import statements into
their Julia equivalents.

Author: JamesWrigley

docs/src/pythoncall-reference.md

@@ -55,6 +55,7 @@ pyhasitem
 pyhash
 pyhelp
 pyimport
+@pyimport_str
 pyin
 pyis
 pyisinstance

src/API/exports.jl

@@ -50,6 +50,7 @@ export pyilshift
 export pyimatmul
 export pyimod
 export pyimport
+export @pyimport_str
 export pyimul
 export pyin
 export pyindex

src/API/macros.jl

@@ -2,6 +2,7 @@
 macro pyconst end
 macro pyeval end
 macro pyexec end
+macro pyimport_str end
 
 # Convert
 macro pyconvert end

src/Core/Core.jl

@@ -34,6 +34,7 @@ import ..PythonCall:
     @pyconst,
     @pyeval,
     @pyexec,
+    @pyimport_str,
     getptr,
     ispy,
     Py,

src/Core/builtins.jl

@@ -1454,13 +1454,153 @@ end
 Import a module `m`, or an attribute `k`, or a tuple of attributes.
 
 If several arguments are given, return the results of importing each one in a tuple.
+
+See also: [`@pyimport_str`](@ref).
 """
 pyimport(m) = pynew(errcheck(@autopy m C.PyImport_Import(m_)))
 pyimport((m, k)::Pair) = (m_ = pyimport(m); k_ = pygetattr(m_, k); pydel!(m_); k_)
 pyimport((m, ks)::Pair{<:Any,<:Tuple}) =
     (m_ = pyimport(m); ks_ = map(k -> pygetattr(m_, k), ks); pydel!(m_); ks_)
 pyimport(m1, m2, ms...) = map(pyimport, (m1, m2, ms...))
 
+"""
+    pyimport"import numpy"
+    pyimport"import numpy as np"
+    pyimport"from numpy import array"
+    pyimport"from numpy import array as arr"
+    pyimport"from numpy import array, zeros"
+    pyimport"from numpy import array as arr, zeros as z"
+    pyimport"import numpy, scipy"
+
+String macro that parses Python import syntax and generates equivalent Julia
+code using [`pyimport()`](@ref). Each form generates `const` bindings in the
+caller's scope.
+
+Multiple lines are supported:
+```julia
+pyimport\"\"\"
+import numpy as np
+from scipy import linalg, optimize
+from os.path import join as pathjoin
+\"\"\"
+
+# Converted to:
+const np = pyimport("numpy")
+const linalg = pyimport("scipy" => "linalg")
+const optimize = pyimport("scipy" => "optimize")
+const pathjoin = pyimport("os.path" => "join")
+```
+
+But multiline or grouped import statements are not supported:
+```julia
+# These will throw an error
+pyimport\"\"\"
+from sys import (path,
+                 version)
+from sys import path, \
+                version
+\"\"\"
+```
+
+Relative imports are also not currently supported.
+"""
+macro pyimport_str(s)
+    esc(_pyimport_parse(s))
+end
+
+function _pyimport_parse(s::AbstractString)
+    lines = filter(!isempty, strip.(split(s, "\n")))
+    isempty(lines) && throw(ArgumentError("pyimport: empty import string"))
+
+    # Check for line continuations
+    for line in lines
+        if contains(line, '\\') || contains(line, '(')
+            throw(ArgumentError("pyimport: line continuation with '\\' or '(' is not supported: $line"))
+        end
+    end
+
+    if length(lines) == 1
+        _pyimport_parse_line(lines[1])
+    else
+        Expr(:block, [_pyimport_parse_line(line) for line in lines]...)
+    end
+end
+
+function _pyimport_parse_line(s::AbstractString)
+    if startswith(s, "from ")
+        _pyimport_parse_from(s)
+    elseif startswith(s, "import ")
+        _pyimport_parse_import(s)
+    else
+        throw(ArgumentError("pyimport: expected 'import ...' or 'from ... import ...', got: $s"))
+    end
+end
+
+function _pyimport_parse_import(s::AbstractString)
+    rest = strip(chopprefix(s, "import"))
+    if isempty(rest)
+        throw(ArgumentError("pyimport: missing module name after 'import'"))
+    end
+
+    parts = split(rest, ","; keepempty=false)
+    exprs = Expr[]
+    for part in parts
+        part = strip(part)
+
+        # Check if there's an `as` clause
+        m = match(r"^(\S+)\s+as\s+(\S+)$", part)
+        if !isnothing(m)
+            # `import numpy.linalg as la` binds la to the linalg submodule
+            modname = m[1]
+            alias = Symbol(m[2])
+            push!(exprs, :(const $alias = pyimport($modname)))
+        else
+            modname = part
+            # `import numpy.linalg` binds numpy (top-level package)
+            # but first imports the submodule to ensure it's loaded
+            dotparts = split(modname, ".")
+            alias = Symbol(dotparts[1])
+            if length(dotparts) == 1
+                push!(exprs, :(const $alias = pyimport($modname)))
+            else
+                toplevel = dotparts[1]
+                push!(exprs, :(const $alias = (pyimport($modname); pyimport($toplevel))))
+            end
+        end
+    end
+
+    length(exprs) == 1 ? exprs[1] : Expr(:block, exprs...)
+end
+
+function _pyimport_parse_from(s::AbstractString)
+    m = match(r"^from\s+(\S+)\s+import\s+(.+)$", s)
+    if isnothing(m)
+        throw(ArgumentError("pyimport: invalid from-import syntax: $s"))
+    end
+
+    modname = m[1]
+    rest = strip(m[2])
+    if rest == "*"
+        throw(ArgumentError("pyimport: wildcard import 'from $modname import *' is not supported"))
+    end
+
+    parts = split(rest, ","; keepempty=false)
+    exprs = Expr[]
+    for part in parts
+        part = strip(part)
+        m2 = match(r"^(\S+)\s+as\s+(\S+)$", part)
+        name, alias = if !isnothing(m2)
+            m2[1], Symbol(m2[2])
+        else
+            part, Symbol(part)
+        end
+
+        push!(exprs, :(const $alias = pyimport($modname => $name)))
+    end
+
+    length(exprs) == 1 ? exprs[1] : Expr(:block, exprs...)
+end
+
 ### builtins not covered elsewhere
 
 """

test/Core.jl

@@ -428,6 +428,79 @@ end
     @test pyis(verpath[2], path)
 end
 
+@testset "pyimport_str" begin
+    parse = PythonCall.Core._pyimport_parse
+
+    # Import a module
+    @test parse("import sys") == :(const sys = pyimport("sys"))
+
+    # Import module as an alias
+    @test parse("import sys as system") == :(const system = pyimport("sys"))
+
+    # Importing a submodule binds the top-level package
+    ex = parse("import os.path") |> Base.remove_linenums!
+    @test ex == :(const os = begin
+                      pyimport("os.path")
+                      pyimport("os")
+                  end) |> Base.remove_linenums!
+
+    # Importing a submodule as an alias binds the submodule
+    @test parse("import os.path as osp") == :(const osp = pyimport("os.path"))
+
+    # import multiple modules
+    ex = parse("import sys, os") |> Base.remove_linenums!
+    @test ex == quote
+        const sys = pyimport("sys")
+        const os = pyimport("os")
+    end |> Base.remove_linenums!
+
+    # from module import name
+    @test parse("from sys import path") == :(const path = pyimport("sys" => "path"))
+
+    # from module import name as alias
+    @test parse("from sys import path as p") == :(const p = pyimport("sys" => "path"))
+
+    # from module import multiple names
+    ex = parse("from sys import path, version") |> Base.remove_linenums!
+    @test ex == quote
+        const path = pyimport("sys" => "path")
+        const version = pyimport("sys" => "version")
+    end |> Base.remove_linenums!
+
+    # from module import multiple names with aliases
+    ex = parse("from sys import path as p, version as v") |> Base.remove_linenums!
+    @test ex == quote
+        const p = pyimport("sys" => "path")
+        const v = pyimport("sys" => "version")
+    end |> Base.remove_linenums!
+
+    # from dotted module import name
+    @test parse("from os.path import join") == :(const join = pyimport("os.path" => "join"))
+
+    # Multiple lines, with extra whitespace
+    ex = parse("import sys \n from    os   import  getcwd  ") |> Base.remove_linenums!
+    @test ex == quote
+        const sys = pyimport("sys")
+        const getcwd = pyimport("os" => "getcwd")
+    end |> Base.remove_linenums!
+
+    # Error cases
+    @test_throws ArgumentError parse("")
+    @test_throws ArgumentError parse("not an import")
+    @test_throws ArgumentError parse("from os import *")
+    @test_throws ArgumentError parse("import")
+
+    # Line continuations are not supported
+    @test_throws ArgumentError parse("from os import \\\n    path, getcwd")
+    @test_throws ArgumentError parse("from os import (\n    path, getcwd\n)")
+
+    # smoke test: actually run the macro
+    m = Module()
+    @eval m using PythonCall
+    @eval m pyimport"import sys"
+    @test pyeq(Bool, m.sys.__name__, "sys")
+end
+
 @testitem "consts" begin
     @test pybuiltins.None isa Py
     @test pystr(String, pybuiltins.None) == "None"