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Beautiful, Idiomatic Python or Don't do this, do this - Raymond Hettinger presentation (pycon 2013)
Replace traditional index manipulation with Python’s core looping idioms.
Learn advanced techniques with for-else clauses and the two argument form of iter().
Clarify function calls with keyword arguments.
Tuple packing and unpacking
Don’t under‐estimate the advantages of updating state variables at the same time. It eliminates an entire class of errors due to out­of-order updates. It allows high level thinking: “chunking”.
Decorators and Context Managers
Helps separate business logic from administrative logic. Clean, beautiful tools for factoring code and improving code reuse. Good naming is essential.
Factor out temporary contexts by using "with" instead of "try/finally".
One logical line of code equals one sentence in English.
Looping over a range of numbers
-------------------------------
Don't do this
for i in [0, 1, 2, 3, 4, 5]:
print i**2
Do this
for i in range(6):
print i**2
Looping over a collection
--------------------------
colors = ['red', 'green', 'blue', 'yellow']
Don't do this
for i in range(len(colors)):
print colors[i]
Do this instead
for color in colors:
print color
(Reversed)
Don't do this
for i in range(len(colors)-1, -1, -1):
print colors[i]
Do this instead
for color in reversed(colors):
print color
Looping over a collection and indicies
--------------------------------------
Don't do this
for i in range(len(colors)):
print i, '-->', colors[i]
Do this instead
for i, color in enumerate(colors):
print i, '-->', color
Looping over two collections
----------------------------
names = ['raymond', 'rachel', 'matthew']
colors = ['red', 'green', 'blue', 'yellow']
for name, color in izip(names, colors):
print name, '-->', color
(Construct a dictionary from these pairs
d = dict(izip(names, colors))
{'matthew': 'blue', 'rachel': 'green', 'raymond': 'red'}
d = dict(enumerate(names))
{0: 'raymond', 1: 'rachel', 2: 'matthew'}
Looping in sorted order
-----------------------
colors = ['red', 'green', 'blue', 'yellow']
for color in sorted(colors):
print color
for color in sorted(colors, reverse=True):
print color
Custom sort order
-----------------
colors = ['red', 'green', 'blue', 'yellow']
Don't do this
def compare_length(c1, c2):
if len(c1) < len(c2): return -1
if len(c1) > len(c2): return 1
return 0
print sorted(colors, cmp=compare_length)
Do this
print sorted(colors, key=len)
Multiple exit points in loops
-----------------------------
Don't do this
def find(seq, target):
found = False
for i, value in enumerate(seq):
if value == tgt:
found = True
break
if not found:
return -1
return i
Do this
def find(seq, target):
for i, value in enumerate(seq):
if value == tgt:
break
else:
return -1
return i
Looping over dictionary keys
----------------------------
d = {'matthew': 'blue', 'rachel': 'green', 'raymond': 'red'}
Don't do this
for k in d:
print k
Or this
for k in d.keys():
if k.startswith('r'):
del d[k]
Do this
d = {k : d[k] for k in d if not k.startswith('r')}
Looping over a dictionary keys and values
-----------------------------------------
Don't do this
for k in d:
print k, '-->', d[k]
Or this
for k, v in d.items():
print k, '-->', v
Do this
for k, v in d.iteritems():
print k, '-->', v
Counting with dictionaries
--------------------------
colors = ['red', 'green', 'red', 'blue', 'green', 'red']
Don't do this
d = {}
for color in colors:
if color not in d:
d[color] = 0
d[color] += 1
{'blue': 1, 'green': 2, 'red': 3}
Or this
d = {}
for color in colors:
d[color] = d.get(color, 0) + 1
Do this
d = defaultdict(int)
for color in colors:
d[color] += 1
List Comprehensions and Generator Expressions
---------------------------------------------
Don't do this
result = []
for i in range(10):
s = i ** 2
result.append(s)
print sum(result)
Do this
print sum(i**2 for i in xrange(10))
Unpacking sequences
-------------------
p = 'Raymond', 'Hettinger', 0x30, 'python@example.com'
Don't do this
fname = p[0]
lname = p[1]
age = p[2]
email = p[3]
Do this
fname, lname, age, email = p
Updating multiple state variables
---------------------------------
Don't do this
def fibonacci(n):
x = 0
y = 1
for i in range(n):
print x
t = y
y = x + y
x = t
Do this
def fibonacci(n):
x, y = 0, 1
for i in range(n):
print x
x, y = y, x+y
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