Go over documentation for Needs, Get, $Path, and $ContextPath (#1826)

Author: rocky

mathics/builtin/directories/user_directories.py

@@ -13,7 +13,7 @@
 
 
 class Path(Predefined):
-    """
+    r"""
     <url>:WMA link:https://reference.wolfram.com/language/ref/Path.html</url>
 
     <dl>
@@ -23,6 +23,13 @@ class Path(Predefined):
 
     >> $Path
      = ...
+
+    '\$Path' used consulted in builtin functions  <url>
+    :\$Get:
+    /doc/reference-of-built-in-symbols/inputoutput-files-and-filesystem/file-and-stream-operations/get/</url>, \
+    and <url>
+    :Needs:
+    /doc/reference-of-built-in-symbols/inputoutput-files-and-filesystem/filesystem-operations/needs/</url> to resolve filenames, and to resolve contexts to file names.
     """
 
     attributes = A_NO_ATTRIBUTES

mathics/builtin/files_io/files.py

@@ -375,9 +375,28 @@ class Get(PrefixOperator):
      = Cos[x] + I Sin[x]
     S> DeleteFile[filename]
 
+    If the 'Path' is not fully qualified built-in variable <url>
+    :\$Path:
+    /doc/reference-of-built-in-symbols/directories-and-directory-operations/user-file-directories/$path/</url> is consulted.
+
+    'Get' can also load packages:
+    >> $ContextPath
+     = ...
+    S> << "VectorAnalysis`"
+     = ...
+
+    If a package is loaded variable <url>
+    :\$ContextPath:
+    /doc/reference-of-built-in-symbols/scoping-constructs/$contextpath/</url> is updated with the new package context name:
+    >> $ContextPath
+     = ...
+
+    See also <url>
+    :Needs:
+    /doc/reference-of-built-in-symbols/inputoutput-files-and-filesystem/filesystem-operations/needs/</url>.
+
+
     ## TODO: Requires EndPackage implemented
-    ## 'Get' can also load packages:
-    ## >> << "VectorAnalysis`"
     """
 
     eval_error = Builtin.generic_argument_error

mathics/builtin/files_io/filesystem.py

@@ -834,6 +834,21 @@ class Needs(Builtin):
     </dl>
 
     >> Needs["VectorAnalysis`"]
+
+    In contrast to <url>
+    :Get:
+    /doc/reference-of-built-in-symbols/inputoutput-files-and-filesystem/file-and-stream-operations/get/</url>, \
+    'Needs' only loads a package if it has not already been loaded.
+
+    Like 'Get',  <url>
+    :\$ContextPath:
+    /doc/reference-of-built-in-symbols/scoping-constructs/$contextpath/</url> is updated \
+    when a new package context is added.
+
+    Builtin variable <url>
+    :\$Path:
+    /doc/reference-of-built-in-symbols/directories-and-directory-operations/user-file-directories/$path/</url> is used resolve the context to a file name.
+
     """
 
     messages = {

mathics/builtin/scoping.py

@@ -316,6 +316,17 @@ class ContextPath_(Predefined):
     ## #> System`$ContextPath
     ##  = {x`}
     ## #> $ContextPath = {"System`", "Global`"};
+
+    Functions <url>
+    :Needs:
+    /doc/reference-of-built-in-symbols/inputoutput-files-and-filesystem/filesystem-operations/needs/</url> and <url>
+    :Get:
+    /doc/reference-of-built-in-symbols/inputoutput-files-and-filesystem/file-and-stream-operations/get/</url>, \
+    add to '\$ContextPath' when a new context is added.
+
+    See also Builtin variable <url>
+    :\$Path:
+    /doc/reference-of-built-in-symbols/directories-and-directory-operations/user-file-directories/$path/</url>.
     """
 
     messages = {"cxlist": "`1` is not a list of valid context names ending in `."}