Issue #4116: Make infile and outfile parameters of flrender script from python-abp optional

abp/filters/sources.py

Index: abp/filters/sources.py
diff --git a/abp/filters/sources.py b/abp/filters/sources.py
index 6aae32c5e5462c300825537c8c787756c4d91a15..a1c9d41a9c7082094abfa6bb161711b585efdd3e 100644
--- a/abp/filters/sources.py
+++ b/abp/filters/sources.py
@@ -17,6 +17,7 @@
 
 import io
 from os import path
+import sys
 
 try:
     from urllib2 import urlopen, HTTPError
@@ -106,6 +107,29 @@ class TopSource(FSSource):
     def _resolve_path(self, path_in_source):
         return path_in_source
 
+    def get(self, path_in_source):
+        """Read the data. Handles stdin, on top of file input.
+
+        Parameters
+        ----------
+        path_in_source : str
+            Path to the file inside of source or '-' for stdin.
+
+        Returns
+        -------
+        generator or str
+            Lines in the file/ from stdin.
+
+        """
+        if path_in_source == '-':
+            lines = sys.stdin.readlines()
+            for line in lines:
+                yield line.rstrip('\n')
+        else:
+            lines = super(TopSource, self).get(path_in_source)
+            for line in lines:
+                yield line
+
 
 class WebSource(object):
     """Handler for http or https.