def extract_functions(content):
try:<EOL><INDENT>return re.findall(function_regexp, content)<EOL><DEDENT>except TypeError:<EOL><INDENT>return []<EOL><DEDENT>
extract all functions from string content, which are in format ${fun()}
    @param (str) content
    @return (list) functions list

    e.g. 
    print(extract_functions('${func(5)}')); # => ["func(5)"]
    print(extract_functions('${func(a=1, b=2)}')); # => ["func(a=1, b=2)"]
    print(extract_functions('${func(a,b,c)}')); # => ['func(a,b,c)']
    print(extract_functions('/api/1000?_t=${get_timestamp()}')); # => ["get_timestamp()"]
    print(extract_functions('/api/${add(1, 2)}')); # => ["add(1, 2)"]
    print(extract_functions("/api/${add(1, 2)}?_t=${get_timestamp()}")); # => ["add(1, 2)", "get_timestamp()"]