Talk I gave at June bangpypers meetup.

Writing better python code.md

Writing better python code

---

Swapping variables

Bad code

>>>a = 23
>>>b = 12
>>>temp = a
>>>a = b
>>>b = temp
>>>print a, b
12, 23

Pythonic

!python
>>>a, b = 23, 12
>>>a, b = b, a
>>>print a, b
12, 23

---

Counting Condition

Bad code

!python

>>>super_users = get_all_superusers_for_organization(org_name)
>>>if len(super_users) > 0:
>>>    print(u"Super users are {}".format(super_users))
>>>else:
>>>    print(u"No super users")

Pythonic

!python

>>>super_users = get_all_superusers_for_organization(org_name)
>>>if super_users:
>>>    print(u"Super users are {}".format(super_users))
>>>else:
>>>    print(u"No super users")

---

Accessing index of list

Bad code

!python

>>>langs = ["Python", "go", "lua"]
>>>index = 0
>>>length = len(langs)
>>>while index < length:
>>>    print(index, langs[index])
>>>    index += 1

Pythonic

!python

>>>langs = ["Python", "go", "lua"]
>>>for index, value in enumerate(langs):
>>>    print(index, value)

---

Check for one condition

Bad code

!python

>>>if user.is_superadmin or user.is_siteadmin or user.is_staff:
>>>    # Grant Access to some page

Pythonic

!python
>>>if any([user.is_superadmin, user.is_siteadmin, user.is_staff]):
>>>    # Grant Access to some page

---

Check for all condition

Bad code

!python

>>>if user.is_superadmin and user.is_siteadmin and user.is_staff:
>>>    # Grant Access to admin page

Pythonic

!python
>>>if all([user.is_superadmin, user.is_siteadmin, user.is_staff]):
>>>    # Grant Access to admin page

---

Range check

Bad code

!python

>>>status_code = requests.post("someurl", params={"foo": "bar"}).status_code
>>>if status_code >= 200 and status_code <= 299:
>>>    print("HTTP call is success")

Pythonic

!python

>>>status_code = request.post("someurl", params={"foo": "bar"}).status_code
>>>if 200 <= status_code <= 299:
>>>    print("HTTP call is success")

---

Is operator

Bad code

!python
>>>250 + 6 is 256
True

>>>250 + 7 is 257
False

Pythonic code

!python
>>>250 + 6 == 256
True

>>>250 + 7 == 257
True

---

Copy a list

Bad code

!python

>>>langs = ["Python", "Go", "Lua"]
>>>new_langs = langs
>>>new_langs.append("Javascript")
>>>print(langs, new_langs)
(['Python', 'Go', 'Lua', 'Javascript'], ['Python', 'Go', 'Lua', 'Javascript'])

Pythonic

!python
>>>langs = ["Python", "Go", "Lua"]
>>>new_langs = langs[:]
>>>new_langs.append("Javascript")
>>>print(langs, new_langs)
(['Python', 'Go', 'Lua'], ['Python', 'Go', 'Lua', 'Javascript'])

---

List comprehension

Bad code

!python

>>>nos = [1, 4, 5, 6]
>>>evens = []
>>>for no in nos:
>>>    if no % 2 == 0:
>>>        evens.append(no)
>>>print(evens)
[4, 6]

Pythonic

!python

>>>nos = [1, 4, 5, 6]
>>>evens = [no for no in nos if no % 2 == 0]
>>>print(evens)
[4, 6]

---

Function defaults

Bad code

!python

>>>def foo():
>>>    return "foo"

>>>def bar(names=[]):
>>>    names.append(foo())
>>>    return names

>>>bar()
["foo"]
>>>bar()
["foo", "foo"]

---

Function defaults ...

Pythonic

!python

>>>def bar(names=None):
>>>   name = foo()
>>>   if not names:
>>>       return [name]
>>>   names.append(name)
>>>   return names

>>>bar()
['foo']
>>>bar()
['foo']

---

Get a element in a dictionary

Bad code

!python

>>>d = {'foo': 'bar'}
>>>if 'baz' in d:
>>>    temp = d['baz']
>>>else:
>>>    temp = ""

Pythonic

!python

>>>d = {'foo': 'bar'}
>>>temp = d.get('baz', "")

---

Frequency count

Bad code

!python

>>>words = ["a", "the", "foo", "bar", "foo"]
>>>frequency = {}
>>>for word in words:
>>>    if word in frequency:
>>>        frequency[word] += 1
>>>    else:
>>>        frequency[word] = 1
>>>print(frequency)
{'a': 1, 'the': 1, 'foo': 2, 'bar': 1}

---

Frequency count ...

Pythonic

!python

>>>from collections import Counter
>>>frequency = Counter(words)
>>>print(frequency)
Counter({'foo': 2, 'a': 1, 'the': 1, 'bar': 1})

---

Raising KeyError in dictionary

Bad code

!python

#Look before you leap
>>>d = {'foo': 'bar'}
>>>if 'baz' in d:
>>>    temp = d['baz']
>>>else:
>>>    raise KeyError("baz is missing")

Pythonic

!python

#Easier to Ask for Forgiveness than Permission
>>>try:
>>>    temp = d["baz"]
>>>except KeyError:
>>>    raise KeyError("baz is missing")

---

Context manager

Bad code

!python

>>>f = open('foo.txt')
>>>print(f.read())
>>>f.close()

Pythonic

!python

>>>with open('foo.txt') as f:
>>>    print(f.read())

---

Iterating over a file

Bad code

!python

>>>with open('foo.txt') as f:
>>>    for line in f.readlines():
>>>        print(line)

Pythonic

!python

>>>with open('foo.txt') as f:
>>>     for line in f:
>>>         print(line)

---

dot accessors

Bad code

!python

>>>class Person(object):
>>>    def __init__(self, name, email):
>>>        self.name = name
>>>        self.email = email
>>>p = Person("kracekumar", "[email protected]")
>>>print(p.name, p.email)
('kracekumar', '[email protected]')

---

dot accessors ...

Pythonic

!python

>>>from collections import namedtuple
>>>Person = namedtuple('Person', ['name', 'email'])
>>>p = Person("kracekumar", "[email protected]")
>>>print(p.name, p.email)
('kracekumar', '[email protected]')

---

Exceptions

Bad code

!python

>>>try:
>>>   foo()
>>>except:
>>>   print("something") # sometimes people write pass. PURE EVIL !

Pythonic

!python

>>>try:
>>>   foo()
>>>except (IndexError, KeyError) as e:
>>>    print("something went wrong")

---

Q & A

---

Thanks

• Email: [email protected]

• Twitter: @kracetheking

If your things to check are already in an iterable, then all and and would be more pythonic. Arguing they're somehow more pythonic over normal or or ands is wrong, and can be less clear for such few conditions (why do I need to construct a list just for this?).

@Ivoz It depends when there are 5 to 6 different conditions to check. Agreed all/any is always preferred with generators.

Good tips, but why is the dot accessors example using a class bad? (Assume there is more in the class than just the example)

Disagree with dot accessors, KeyError raising for dicts, any and all are preferences.