Improve function cache error message #992
Description
Problem
app.py:
import datetime
import streamlit as st
def bar():
return datetime.strptime("12", "%H")
@st.cache
def foo():
return bar()
def main():
foo()
if __name__ == '__main__':
main()streamlit run app.py
The error message in the browser:
Streamlit failed to hash an object of type <class 'function'>.
...
TypeError: object supporting the buffer API required
Traceback:
File "/home/ole/.miniconda3/envs/streamlit-pg/lib/python3.7/site-packages/streamlit/ScriptRunner.py", line 324, in _run_script
exec(code, module.__dict__)
File "/home/ole/src/streamlit_test/app.py", line 15, in <module>
main()
File "/home/ole/src/streamlit_test/app.py", line 12, in main
foo()
File "/home/ole/.miniconda3/envs/streamlit-pg/lib/python3.7/site-packages/streamlit/caching.py", line 463, in wrapped_func
return get_or_set_cache()
File "/home/ole/.miniconda3/envs/streamlit-pg/lib/python3.7/site-packages/streamlit/caching.py", line 432, in get_or_set_cache
code_hasher.update(func)
File "/home/ole/.miniconda3/envs/streamlit-pg/lib/python3.7/site-packages/streamlit/hashing.py", line 211, in update
self._update(self.hasher, obj, context)
File "/home/ole/.miniconda3/envs/streamlit-pg/lib/python3.7/site-packages/streamlit/hashing.py", line 243, in _update
hasher.update(b)
To me it's hard to guess from the reported error that the cause is a "compile" error inside bar
Wrapping the content of _code_to_bytes in hashing.py in a try catch reveals the real error - in this case very helpful:
AttributeError: module 'datetime' has no attribute 'strptime'
Solution
Somehow collect the root-cause exception and display that in the browser. Bonus if more info is collect, like the associated function name (in case of function hashing)