lammps.py errors (#4458)

* contributes to #3925
* fix lammps.py doctest errors

package/MDAnalysis/coordinates/LAMMPS.py

@@ -66,22 +66,33 @@
 :class:`~MDAnalysis.topology.LAMMPSParser.DATAParser`) together with a
 LAMMPS DCD with "*real*" provide the keyword *format="LAMMPS*"::
 
-    >>> u = MDAnalysis.Universe("lammps.data", "lammps_real.dcd", format="LAMMPS")
+    >>> import MDAnalysis
+    >>> from MDAnalysis.tests.datafiles import LAMMPSdata2, LAMMPSdcd2
+    >>> u = MDAnalysis.Universe(LAMMPSdata2, LAMMPSdcd2, format="LAMMPS")
 
-If the trajectory uses *units nano* then use ::
+If the trajectory uses *units nano* then use
 
-    >>> u = MDAnalysis.Universe("lammps.data", "lammps_nano.dcd", format="LAMMPS",
+    >>> import MDAnalysis
+    >>> from MDAnalysis.tests.datafiles import LAMMPSdata2, LAMMPSdcd2
+    >>> u = MDAnalysis.Universe(LAMMPSdata2, LAMMPSdcd2, format="LAMMPS",
     ...                          lengthunit="nm", timeunit="ns")
 
 To scan through a trajectory to find a desirable frame and write to a LAMMPS
 data file,
 
->>> for ts in u.trajectory:
-...     # analyze frame
-...     if take_this_frame == True:
-...         with mda.Writer('frame.data') as W:
-...             W.write(u.atoms)
-...         break
+   >>> import MDAnalysis
+   >>> from MDAnalysis.tests.datafiles import LAMMPSdata2, LAMMPSdcd2 
+   >>> u = MDAnalysis.Universe(LAMMPSdata2, LAMMPSdcd2, format="LAMMPS",
+   ...                          lengthunit="nm", timeunit="ns")
+   >>> take_this_frame = False
+   >>> for ts in u.trajectory:
+   ...     # analyze frame
+   ...     if ts.frame == 4:
+   ...         take_this_frame = True
+   ...     if take_this_frame == True:
+   ...         with MDAnalysis.Writer('frame.data') as W:
+   ...             W.write(u.atoms)
+   ...         break
 
 Note
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