Avoid using reserved word in variable names

[hupili]

FAQ: https://github.com/hupili/python-for-data-and-media-communication-gitbook/blob/master/python-language-basics.md#name-clash-with-reserved-word

• [x] https://github.com/hupili/python-for-data-and-media-communication-gitbook/blob/master/notes-week-10.md#word-frequency
• [x] Scan the entire notebook for similar use.

[ChicoXYC]

@hupili update --> b84b9ae scan the whole document, replacing conflict word in variable names. Including str, dict, list.

[hupili]

list1 is not good. That let's people think list could be a valid name. Please use mylist if you can not find a proper name.

If there is a physical meaning, we usually embed the physical meaning in the variable name. For example, if you have a list of articles, either say articles = [] or article_list = [].

[ChicoXYC]

update ea3c183