gistfile1.txt

# Fix no spaces after opening braces
\{([\{|%])(\w+) -> {\1 \2

# Fix no spaces before closing braces
([\w']+)([}|%])\} -> \1 \2}

# Test cases
{{ row 1 }}
{{row2}}
{% row 3 %}
{%row 4%}

# Sed replacement
sed s/'{\([{%]\)\([^ ]\)/{\1 \2'/g testfile.py