Add docstrings for read_py_file and read_py_url.

IPython/utils/openpy.py

@@ -1,162 +1,192 b''
 """
 Tools to open .py files as Unicode, using the encoding specified within the file,
 as per PEP 263.
 
 Much of the code is taken from the tokenize module in Python 3.2.
 """
 from __future__ import absolute_import
 
 import __builtin__
 import io
 from io import TextIOWrapper
 import re
 import urllib
 
 cookie_re = re.compile(ur"coding[:=]\s*([-\w.]+)", re.UNICODE)
 cookie_comment_re = re.compile(ur"^\s*#.*coding[:=]\s*([-\w.]+)", re.UNICODE)
 
 try:
     # Available in Python 3
     from tokenize import detect_encoding
 except ImportError:
     from codecs import lookup, BOM_UTF8
     
     # Copied from Python 3.2 tokenize
     def _get_normal_name(orig_enc):
         """Imitates get_normal_name in tokenizer.c."""
         # Only care about the first 12 characters.
         enc = orig_enc[:12].lower().replace("_", "-")
         if enc == "utf-8" or enc.startswith("utf-8-"):
             return "utf-8"
         if enc in ("latin-1", "iso-8859-1", "iso-latin-1") or \
            enc.startswith(("latin-1-", "iso-8859-1-", "iso-latin-1-")):
             return "iso-8859-1"
         return orig_enc
     
     # Copied from Python 3.2 tokenize
     def detect_encoding(readline):
         """
         The detect_encoding() function is used to detect the encoding that should
         be used to decode a Python source file.  It requires one argment, readline,
         in the same way as the tokenize() generator.
 
         It will call readline a maximum of twice, and return the encoding used
         (as a string) and a list of any lines (left as bytes) it has read in.
 
         It detects the encoding from the presence of a utf-8 bom or an encoding
         cookie as specified in pep-0263.  If both a bom and a cookie are present,
         but disagree, a SyntaxError will be raised.  If the encoding cookie is an
         invalid charset, raise a SyntaxError.  Note that if a utf-8 bom is found,
         'utf-8-sig' is returned.
 
         If no encoding is specified, then the default of 'utf-8' will be returned.
         """
         bom_found = False
         encoding = None
         default = 'utf-8'
         def read_or_stop():
             try:
                 return readline()
             except StopIteration:
                 return b''
 
         def find_cookie(line):
             try:
                 line_string = line.decode('ascii')
             except UnicodeDecodeError:
                 return None
 
             matches = cookie_re.findall(line_string)
             if not matches:
                 return None
             encoding = _get_normal_name(matches[0])
             try:
                 codec = lookup(encoding)
             except LookupError:
                 # This behaviour mimics the Python interpreter
                 raise SyntaxError("unknown encoding: " + encoding)
 
             if bom_found:
                 if codec.name != 'utf-8':
                     # This behaviour mimics the Python interpreter
                     raise SyntaxError('encoding problem: utf-8')
                 encoding += '-sig'
             return encoding
 
         first = read_or_stop()
         if first.startswith(BOM_UTF8):
             bom_found = True
             first = first[3:]
             default = 'utf-8-sig'
         if not first:
             return default, []
 
         encoding = find_cookie(first)
         if encoding:
             return encoding, [first]
 
         second = read_or_stop()
         if not second:
             return default, [first]
 
         encoding = find_cookie(second)
         if encoding:
             return encoding, [first, second]
 
         return default, [first, second]
 
 try:
     # Available in Python 3.2 and above.
     from tokenize import open
 except ImportError:
     # Copied from Python 3.2 tokenize
     def open(filename):
         """Open a file in read only mode using the encoding detected by
         detect_encoding().
         """
         buffer = io.open(filename, 'rb')   # Tweaked to use io.open for Python 2
         encoding, lines = detect_encoding(buffer.readline)
         buffer.seek(0)
         text = TextIOWrapper(buffer, encoding, line_buffering=True)
         text.mode = 'r'
         return text   
 
 def strip_encoding_cookie(filelike):
     """Generator to pull lines from a text-mode file, skipping the encoding
     cookie if it is found in the first two lines.
     """
     it = iter(filelike)
     try:
         first = next(it)
         if not cookie_comment_re.match(first):
             yield first
         second = next(it)
         if not cookie_comment_re.match(second):
             yield second
     except StopIteration:
         return
     
     for line in it:
         yield line
 
-def read_py_file(filename, errors='replace', skip_encoding_cookie=True):
+def read_py_file(filename, skip_encoding_cookie=True):
+    """Read a Python file, using the encoding declared inside the file.
+    
+    Parameters
+    ----------
+    filename : str
+      The path to the file to read.
+    skip_encoding_cookie : bool
+      If True (the default), and the encoding declaration is found in the first
+      two lines, that line will be excluded from the output - compiling a
+      unicode string with an encoding declaration is a SyntaxError in Python 2.
+    
+    Returns
+    -------
+    A unicode string containing the contents of the file.
+    """
     with open(filename) as f:   # the open function defined in this module.
         if skip_encoding_cookie:
             return "".join(strip_encoding_cookie(f))
         else:
             return f.read()
 
 def read_py_url(url, errors='replace', skip_encoding_cookie=True):
-    """Open a URL to a raw Python file, using the encoding detected by
-    detect_encoding().
+    """Read a Python file from a URL, using the encoding declared inside the file.
+    
+    Parameters
+    ----------
+    url : str
+      The URL from which to fetch the file.
+    errors : str
+      How to handle decoding errors in the file. Options are the same as for
+      bytes.decode(), but here 'replace' is the default.
+    skip_encoding_cookie : bool
+      If True (the default), and the encoding declaration is found in the first
+      two lines, that line will be excluded from the output - compiling a
+      unicode string with an encoding declaration is a SyntaxError in Python 2.
+    
+    Returns
+    -------
+    A unicode string containing the contents of the file.
     """
     response = urllib.urlopen(url)
     buffer = io.BytesIO(response.read())
     encoding, lines = detect_encoding(buffer.readline)
     buffer.seek(0)
     text = TextIOWrapper(buffer, encoding, errors=errors, line_buffering=True)
     text.mode = 'r'
     if skip_encoding_cookie:
         return "".join(strip_encoding_cookie(text))
     else:
         return text.read()