fixed issues regarding ipython notebooks

Hektor will no longer attempt to parse empty files as ipython notebooks.
Long outputs will be truncated to 50 lines at most.

.gitignore

 /target
 **/*.rs.bk
 *.json
+
+.idea

src/input_types/ipynb.rs

@@ -158,6 +158,8 @@ pub struct CodeCell {
     pub execution_count: Option<i64>,
 }
 
+const MAX_OUTPUT_LINES: usize = 50;
+
 impl Display for CodeCell {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
         let exec_count_as_str = self
@@ -168,8 +170,33 @@ impl Display for CodeCell {
         writeln!(f, "{}\n", self.source)?;
 
         writeln!(f, "# Out[{}]:\n", exec_count_as_str)?;
+
+        let mut has_stream_output = false;
         for output in &self.outputs {
-            writeln!(f, "{}", comment_out(output.to_string()))?;
+            let mut out_str = output.to_string();
+
+            // IPython batches stream outputs if they are too long
+            // we only want to show the first batch of stream outputs.
+            // Also, we want to truncate too long output streams.
+            if let Output::Stream(stream) = output {
+                if has_stream_output {
+                    continue;
+                }
+                has_stream_output = true;
+
+                out_str = stream
+                    .to_string()
+                    .lines()
+                    .take(MAX_OUTPUT_LINES)
+                    .collect::<Vec<_>>()
+                    .join("\n");
+
+                if out_str.lines().count() == MAX_OUTPUT_LINES {
+                    out_str.push_str("\nOUTPUT HAS BEEN TRUNCATED. SEE ORIGINAL NOTEBOOK FOR FULL OUTPUT.");
+                }
+            }
+
+            writeln!(f, "{}", comment_out(out_str))?;
         }
         Ok(())
     }

src/transform/submissions.rs

@@ -49,7 +49,7 @@ pub fn transform_submissions(
             tests: vec![],
         };
 
-        if sub_type.programming_language == ProgrammingLang::Python {
+        if sub_type.programming_language == ProgrammingLang::Python && submission.code.len() > 0 {
             render_code::<Notebook>(&mut submission)?;
         }
         Ok(submission)