python · serhiy-storchaka · Apr 5, 2017 · Oct 12, 2017 · Oct 12, 2017
diff --git a/Doc/library/pprint.rst b/Doc/library/pprint.rst
@@ -30,7 +30,7 @@ The :mod:`pprint` module defines one class:
 .. First the implementation class:
 
 
-.. class:: PrettyPrinter(indent=1, width=80, depth=None, stream=None, *, \
+.. class:: PrettyPrinter(indent=1, width=None, depth=None, stream=None, *, \
                          compact=False)
 
    Construct a :class:`PrettyPrinter` instance.  This constructor understands
@@ -44,7 +44,9 @@ The :mod:`pprint` module defines one class:
    controlled by *depth*; if the data structure being printed is too deep, the next
    contained level is replaced by ``...``.  By default, there is no constraint on
    the depth of the objects being formatted.  The desired output width is
-   constrained using the *width* parameter; the default is 80 characters.  If a
+   constrained using the *width* parameter, or the width of the terminal if
+   an output stream is interactive (i.e., connected to a
+   terminal/tty device), or by 80 characters.  If a
    structure cannot be formatted within the constrained width, a best effort will
    be made.  If *compact* is false (the default) each item of a long sequence
    will be formatted on a separate line.  If *compact* is true, as many items
@@ -76,6 +78,9 @@ The :mod:`pprint` module defines one class:
       >>> pp.pprint(tup)
       ('spam', ('eggs', ('lumberjack', ('knights', ('ni', ('dead', (...)))))))
 
+   .. versionchanged:: 3.7
+      The width of the terminal is used if an output stream is interactive.
+
 
 The :mod:`pprint` module also provides several shortcut functions:
 
@@ -89,7 +94,7 @@ The :mod:`pprint` module also provides several shortcut functions:
       Added the *compact* parameter.
 
 
-.. function:: pprint(object, stream=None, indent=1, width=80, depth=None, *, \
+.. function:: pprint(object, stream=None, indent=1, width=None, depth=None, *, \
                      compact=False)
 
    Prints the formatted representation of *object* on *stream*, followed by a
@@ -113,6 +118,9 @@ The :mod:`pprint` module also provides several shortcut functions:
        'knights',
        'ni']
 
+   .. versionchanged:: 3.7
+      The width of the terminal is used if an output stream is interactive.
+
 
 .. function:: isreadable(object)
 

diff --git a/Lib/pprint.py b/Lib/pprint.py
@@ -39,12 +39,13 @@
 import sys as _sys
 import types as _types
 from io import StringIO as _StringIO
+from os import get_terminal_size as _get_terminal_size
 
 __all__ = ["pprint","pformat","isreadable","isrecursive","saferepr",
            "PrettyPrinter"]
 
 
-def pprint(object, stream=None, indent=1, width=80, depth=None, *,
+def pprint(object, stream=None, indent=1, width=None, depth=None, *,
            compact=False):
     """Pretty-print a Python object to a stream [default is sys.stdout]."""
     printer = PrettyPrinter(
@@ -96,7 +97,7 @@ def _safe_tuple(t):
     return _safe_key(t[0]), _safe_key(t[1])
 
 class PrettyPrinter:
-    def __init__(self, indent=1, width=80, depth=None, stream=None, *,
+    def __init__(self, indent=1, width=None, depth=None, stream=None, *,
                  compact=False):
         """Handle pretty printing operations onto a stream using a set of
         configured parameters.
@@ -118,21 +119,30 @@ def __init__(self, indent=1, width=80, depth=None, stream=None, *,
             If true, several items will be combined in one line.
 
         """
+        if stream is None:
+            stream = _sys.stdout
         indent = int(indent)
-        width = int(width)
         if indent < 0:
             raise ValueError('indent must be >= 0')
         if depth is not None and depth <= 0:
             raise ValueError('depth must be > 0')
+        if width is None:
+            width = 80
+            if hasattr(stream, 'isatty') and stream.isatty():
+                try:
+                    width = _get_terminal_size(stream.fileno()).columns
+                except (AttributeError, ValueError, OSError):
+                    # stream doesn't have a fileno, or is closed, detached, or
+                    # not a terminal, or os.get_terminal_size() is unsupported
+                    pass
+        else:
+            width = int(width)
         if not width:
             raise ValueError('width must be != 0')
         self._depth = depth
         self._indent_per_level = indent
         self._width = width
-        if stream is not None:
-            self._stream = stream
-        else:
-            self._stream = _sys.stdout
+        self._stream = stream
         self._compact = bool(compact)
 
     def pprint(self, object):

diff --git a/Lib/test/test_pprint.py b/Lib/test/test_pprint.py
@@ -345,7 +345,7 @@ def test_subclassing(self):
         exp = """\
 {'names with spaces': 'should be presented using repr()',
  others.should.not.be: like.this}"""
-        self.assertEqual(DottedPrettyPrinter().pformat(o), exp)
+        self.assertEqual(DottedPrettyPrinter(width=80).pformat(o), exp)
 
     def test_set_reprs(self):
         self.assertEqual(pprint.pformat(set()), 'set()')

diff --git a/Misc/NEWS.d/next/Library/2017-10-12-23-43-02.bpo-29996.kQ198U.rst b/Misc/NEWS.d/next/Library/2017-10-12-23-43-02.bpo-29996.kQ198U.rst
@@ -0,0 +1,2 @@
+The width of the terminal is now used as default width in pprint() if the
+output stream is connected to a terminal.
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		The width of the terminal is now used as default width in pprint() if the
		output stream is connected to a terminal.