Limit length of dataarray reprs (#3905)

* limit length of dataarray reprs

* repr depends on numpy versions

* whatsnew

* correct comment based on @keewis comment

* Update whats-new.rst

Co-authored-by: Deepak Cherian <dcherian@users.noreply.github.com>

doc/whats-new.rst

@@ -66,6 +66,9 @@ New Features
 - Limited the length of array items with long string reprs to a
   reasonable width (:pull:`3900`)
   By `Maximilian Roos <https://github.com/max-sixty>`_
+- Limited the number of lines of large arrays when numpy reprs would have greater than 40.
+  (:pull:`3905`)
+  By `Maximilian Roos <https://github.com/max-sixty>`_
 - Implement :py:meth:`DataArray.idxmax`, :py:meth:`DataArray.idxmin`,
   :py:meth:`Dataset.idxmax`, :py:meth:`Dataset.idxmin`.  (:issue:`60`, :pull:`3871`)
   By `Todd Jennings <https://github.com/toddrjen>`_
@@ -96,7 +99,6 @@ New Features
   By `Deepak Cherian <https://github.com/dcherian>`_
 - :py:meth:`map_blocks` can now handle dask-backed xarray objects in ``args``. (:pull:`3818`)
   By `Deepak Cherian <https://github.com/dcherian>`_
-
 - Add keyword ``decode_timedelta`` to :py:func:`xarray.open_dataset`,
   (:py:func:`xarray.open_dataarray`, :py:func:`xarray.open_dataarray`,
   :py:func:`xarray.decode_cf`) that allows to disable/enable the decoding of timedeltas

xarray/core/formatting.py

@@ -3,7 +3,7 @@
 import contextlib
 import functools
 from datetime import datetime, timedelta
-from itertools import zip_longest
+from itertools import chain, zip_longest
 from typing import Hashable
 
 import numpy as np
@@ -422,6 +422,17 @@ def set_numpy_options(*args, **kwargs):
         np.set_printoptions(**original)
 
 
+def limit_lines(string: str, *, limit: int):
+    """
+    If the string is more lines than the limit,
+    this returns the middle lines replaced by an ellipsis
+    """
+    lines = string.splitlines()
+    if len(lines) > limit:
+        string = "\n".join(chain(lines[: limit // 2], ["..."], lines[-limit // 2 :]))
+    return string
+
+
 def short_numpy_repr(array):
     array = np.asarray(array)
 
@@ -447,7 +458,7 @@ def short_data_repr(array):
     elif hasattr(internal_data, "__array_function__") or isinstance(
         internal_data, dask_array_type
     ):
-        return repr(array.data)
+        return limit_lines(repr(array.data), limit=40)
     elif array._in_memory or array.size < 1e5:
         return short_numpy_repr(array)
     else:

xarray/tests/test_formatting.py

@@ -405,10 +405,19 @@ def test_short_numpy_repr():
         np.random.randn(20, 20),
         np.random.randn(5, 10, 15),
         np.random.randn(5, 10, 15, 3),
+        np.random.randn(100, 5, 1),
     ]
     # number of lines:
-    # for default numpy repr: 167, 140, 254, 248
-    # for short_numpy_repr: 1, 7, 24, 19
+    # for default numpy repr: 167, 140, 254, 248, 599
+    # for short_numpy_repr: 1, 7, 24, 19, 25
     for array in cases:
         num_lines = formatting.short_numpy_repr(array).count("\n") + 1
         assert num_lines < 30
+
+
+def test_large_array_repr_length():
+
+    da = xr.DataArray(np.random.randn(100, 5, 1))
+
+    result = repr(da).splitlines()
+    assert len(result) < 50