DOC: Add warning for newbs not to edit auto-generated file, #10456

Author: Garrett-R

pandas/src/generate_code.py

@@ -1,12 +1,24 @@
+"""
+This file generates `generated.pyx` which is then included in `../algos.pyx`
+during building.  To regenerate `generated.pyx`, just run:
+
+    `python generate_code.py`.
+
+"""
+
 from __future__ import print_function
-# we only need to be able to run this file on 2.7
-# don't introduce a pandas/pandas.compat import
-# or we get a bootstrapping problem
-from StringIO import StringIO
+import os
+from pandas.compat import StringIO
 import numpy as np
 
 _int64_max = np.iinfo(np.int64).max
 
+warning_to_new_contributors = """
+# DO NOT EDIT THIS FILE: This file was autogenerated from generate_code.py, so
+# please edit that file and then run `python2 generate_code.py` to re-generate
+# this file.
+"""
+
 header = """
 cimport numpy as np
 cimport cython
@@ -2580,8 +2592,14 @@ def generate_from_template(template, exclude=None):
                   take_2d_multi_template]
 
 
-def generate_take_cython_file(path='generated.pyx'):
+def generate_take_cython_file():
+    # Put `generated.pyx` in the same directory as this file
+    directory = os.path.dirname(os.path.realpath(__file__))
+    filename = 'generated.pyx'
+    path = os.path.join(directory, filename)
+
     with open(path, 'w') as f:
+        print(warning_to_new_contributors, file=f)
         print(header, file=f)
 
         print(generate_ensure_dtypes(), file=f)

pandas/src/generated.pyx

@@ -1,4 +1,9 @@
 
+# DO NOT EDIT THIS FILE: This file was autogenerated from generate_code.py, so
+# please edit that file and then run `python2 generate_code.py` to re-generate
+# this file.
+
+
 cimport numpy as np
 cimport cython