Handle case where prompt number is not defined in latex templates

IPython/nbconvert/templates/latex/style_bw_ipython.tplx

@@ -1,41 +1,45 b''
 ((= Black&white ipython input/output style =))
 
 ((*- extends 'base.tplx' -*))
 
 %===============================================================================
 % Input
 %===============================================================================
 
 ((* block input scoped *))
 ((( add_prompt(cell.input, cell, 'In ') )))
 ((* endblock input *))
 
 
 %===============================================================================
 % Output
 %===============================================================================
 
 ((* block pyout scoped *))
     ((*- for type in output | filter_data_type -*))
         ((*- if type in ['text']*))
 ((( add_prompt(output.text, cell, 'Out') )))
         ((*- else -*))
 \verb+Out[((( cell.prompt_number )))]:+((( super() )))
         ((*- endif -*))
     ((*- endfor -*))
 ((* endblock pyout *))
 
 
 %==============================================================================
 % Support Macros
 %==============================================================================
 
 % Name: draw_prompt
 % Purpose: Renders an output/input prompt
 ((* macro add_prompt(text, cell, prompt) -*))
+    ((*- if cell.prompt_number is defined -*))
     ((*- set prompt_number = "" ~ (cell.prompt_number | replace(None, " ")) -*))
+    ((*- else -*))
+    ((*- set prompt_number = " " -*))
+    ((*- endif -*))
     ((*- set indentation = " " * (prompt_number | length + 7) -*))
 \begin{verbatim}
 (((- text | add_prompts(first=prompt ~ '[' ~ prompt_number ~ ']: ', cont=indentation) -)))
 \end{verbatim}
 ((*- endmacro *))

IPython/nbconvert/templates/latex/style_ipython.tplx

@@ -1,54 +1,58 b''
 ((= IPython input/output style =))
 
 ((*- extends 'base.tplx' -*))
 
 % Custom definitions
 ((* block definitions *))
     ((( super() )))
 
     % Pygments definitions
     ((( resources.latex.pygments_definitions )))
 
     % Exact colors from NB
     \definecolor{incolor}{rgb}{0.0, 0.0, 0.5}
     \definecolor{outcolor}{rgb}{0.545, 0.0, 0.0}
 
 ((* endblock definitions *))
 
 %===============================================================================
 % Input
 %===============================================================================
 
 ((* block input scoped *))
     ((( add_prompt(cell.input | highlight2latex(strip_verbatim=True), cell, 'In ', 'incolor') )))
 ((* endblock input *))
 
 
 %===============================================================================
 % Output
 %===============================================================================
 
 ((* block pyout scoped *))
     ((*- for type in output | filter_data_type -*))
         ((*- if type in ['text']*))
             ((( add_prompt(output.text | escape_latex, cell, 'Out', 'outcolor') )))
         ((* else -*))
 \texttt{\color{outcolor}Out[{\color{outcolor}((( cell.prompt_number )))}]:}((( super() )))
         ((*- endif -*))
     ((*- endfor -*))
 ((* endblock pyout *))
 
 
 %==============================================================================
 % Support Macros
 %==============================================================================
 
 % Name: draw_prompt
 % Purpose: Renders an output/input prompt
 ((* macro add_prompt(text, cell, prompt, prompt_color) -*))
+    ((*- if cell.prompt_number is defined -*))
     ((*- set prompt_number = "" ~ (cell.prompt_number | replace(None, " ")) -*))
+    ((*- else -*))
+    ((*- set prompt_number = " " -*))
+    ((*- endif -*))
     ((*- set indention =  " " * (prompt_number | length + 7) -*))
 \begin{Verbatim}[commandchars=\\\{\}]
 ((( text | add_prompts(first='{\color{' ~ prompt_color ~ '}' ~ prompt ~ '[{\\color{' ~ prompt_color ~ '}' ~ prompt_number ~ '}]:} ', cont=indention) )))
 \end{Verbatim}
 ((*- endmacro *))