Common Python Mistakes

Originally named "Common Newbie Mistakes in Python" then I realized I still make these mistakes. Wait. I guess that still makes me a newbie.

First presented at PizzaPy - Feb 25, 2014.

Transcript

1. Common Newbie Mistakes in Python D. Yu
2. Let’s start with something “obvious” if dict.has_key(key) pass
3. Let’s start with something “obvious” The joys of correct-looking code!
4. The joys of correct-looking code: if dict.has_key(key): pass
5. Checking for a key inside a dict. if dict.has_key(key): pass
6. Checking for a key inside a dict. has_key() was deprecated a long time ago
7. Checking for a key inside a dict. if key in dict: pass
8. Checking if a list is empty. # l is a list if l != None and len(l) > 0 : pass
9. Checking if a list is empty. Not necessarily a problem, but it’s not idiomatic.
10. Checking if a list is empty. # l is a list if l: pass
11. Single item tuples. (‘hey_there’)
12. Single item tuples. The constructor for tuples? It’s not a pair of parentheses.
13. Single item tuples. (‘hey_there’,)
14. Indices in a list. for i in range(len(l)): print l[i]
15. Indices in a list. You don’t really need to access the index.
16. Indices in a list. for i in l: print i # If you really want indices: for i, item in enumerate(l): print i, item
17. Importing everything: from yo_package import *
18. Importing everything: This pollutes the global namespace.
19. Importing everything: from yo_package import yesyesyo import yo_package
20. Iterating over a dict and deleting items. for k, v in d.iteritems(): if k == x: del d[k]
21. Iterating over a dict and deleting items. You can’t delete items in a dict while iterating over it. This causes a RunTimeError in Python. Sometimes leads to unpredictable behavior in other languages.
22. Iterating over a dict and deleting items. for k in d.keys(): if d[k] == x: del d[k]
23. END