Today I will summarize some of the commonly used style codes in python. These may be used by everyone, but sometimes they may be forgotten. I summarize here for your reference~~~

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The title traverses a range of numbers

for i in xrange(6):
    print i ** 2

xrange will return an iterator, which is used to traverse a range one value at a time, which saves more memory than range. Xrange has been renamed range in python3.

Iterate over the collection

colors = ['red', 'green', 'blue', 'yellow']
for color in colors:
    print color

Traverse the collection in reverse

for color in reversed(colors):
    print color

Traverse the collection and its subscripts

for i, color in enumerate(colors):
    print i, '-->', color

Traverse two sets

names = ['raymond', 'rachel', 'mattthew']
colors = ['red', 'green', 'blue', 'yellow']
for name, color in izip(names, colors):
    print name, '-->', color

Zip generates a new list in memory and requires more memory. izip is more efficient than zip. In python3, izip was renamed to zip, replacing the original zip as a built-in function.

Orderly traversal

colors = ['red', 'green', 'blue', 'yellow']
for color in sorted(colors):
    print color
for color in sorted(coloes, reverse = True):
    print color

Custom sort order

colors = ['red', 'green', 'blue', 'yellow']
print sorted(colors, key=len)

List comprehensions and generators

print sum(i ** 2 for i in xrange(10))

Identify multiple exit points within the loop

def find(seq, target):
    for i, value in enumerate(seq):
        if value == target:
            break
    else:
        return -1
    return i

Separate temporary context

with open('help.txt', 'w') as f:
    with redirect_stdout(f):
        help(pow)

The above code is used to demonstrate how to temporarily redirect standard output to a file, and then return to normal. Note that redirect_stdout was added in python3.4.

Open and close files

with open('data.txt') as f:
    data = f.read()

Use lock

lock = threading.Lock()
with lock:
    print 'critical section 1'
    print 'critical section 2'

Count with dictionary

colors = ['red', 'green', 'red', 'blue', 'green', 'red']

d = {
    
    }
for color in colors:
    d[color] = d.get(color, 0) + 1

d = defaultdict(int)
for color in colors:
    d[color] += 1

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Python style code collection