Responsiveness, interactive ipython
console, and versatile, customizable design (not like Jupyter Notebook which locks you into browser); I need full control on editor color scheme, syntax coloring, bracket matching and full debugger support with breakpoints. Great support of scientific plotting is also required.
Do not propose: SpyderIDE (bugged breakpoint support, crashes); JetBrains PyCharm with JupyterNotebooks plugin (doesn't work); SublimeText/LightTable/AtomIDE/VScode (no or limited debugger support).
Something like Geany or CodeBlocks will do, if all requirements are met.