New tricks

[brennerm]

[agumonkey]

Tuples

tuple syntax

a = 1

# >>> a
# 1
# >>> a, 
# (1, )

unpacking iterable of length 1

a, = (1, )

unpacking with starred expression

a,*b,c = range(10)

# >>> a
# 0
# >>> b
# [1, 2, 3, 4, 5, 6, 7, 8]
# >>> c
# 9

a,*b,d,e,f = range(10)

# >>> (a,b,c,d,e,f)
# (0, [1, 2, 3, 4, 5, 6], 9, 7, 8, 9)

[obeleh]

loop over dicts that share (some) keys

dctA = {'a': 1, 'b': 2, 'c': 3}
dctB = {'b': 4, 'c': 5, 'd': 6}

for ky in set(dctA) & set(dctB):
    print ky

this one is much slower:

for ky in dctA:
    if ky in dctB:
        print ky

[obeleh]

lookup deep nested value in dicts

nested = {'a': {'b': {'c': {'d': 1}}}}

print nested.get('a', {}).get('b', {}).get('c', {}).get('d')
print nested.get('x', {}).get('y', {}).get('z', {}).get('0')

This is almost just as fast as completly testing whether the variable exists and IMO more readable.

[obeleh]

Copy lists

a = [1, 2, 3, 4, 5]
cpyA = list(a)
cpyB = a[:]

cpyB is faster

[obeleh]

Startswith

lst = range(10000)


def string_startswith():
    for _ in lst:
        'blasdfsf'.startswith('__')
        '__aqqqqqqqqqqqqqqqqqsdfsf'.startswith('__')


def string_eq_first_two():
    for _ in lst:
        'blasdfsf'[:2] == '__'
        '__aqqqqqqqqqqqqqqqqqsdfsf'[:2] == '__'

The second one is faster

[brennerm]

Hey agumonkey,
thanks for your contribution. I added your last example to the collection.
Your first two examples doesn't really show off a trick to me, that's why I didn't add them.
Anyway, thanks for your support.

[brennerm]

Hey obeleh,
thanks for your contribution. From your examples I added two to the collection.
The remaining are good to know as well, but I'm not looking for code snippets, that concentrate on performance.
Anyway, thanks for your support.

[agumonkey]

@brennerm

They sit between tricks and easy to overlook syntax. Here's another thing I only found recently:

slice operator accepts None

# useful to have a value to denote unknown lengths
#
# here with range pairs

ranges = [(0,6), (6,None)]
for beg,end in ranges:
    print('aabbccddeeff'[beg:end])

[brennerm]

@agumonkey
Yeah you can use [0:None], but you can write it like this as well:

print('aabbccddeeff'[0:])

For me this is more readable.

[agumonkey]

@brennerm

It's unrelated, ability to pass a a value to [:] is rarely shown and very valuable. (see this example).

[bash-j]

Never seen this trick before so I played around a bit.
Named formatting, more examples:

d = {'Jeff Smith': {'name': 'Jeff', 'age': 24}}
person = 'Jeff Smith'
print("My name is {name} and I'm {age} years old.".format(**d[person]))

Is it possible to do something like the following (which doesn't work)?

d = {'Jeff Smith': {'name': 'Jeff', 'age': {'years': 24, 'decades': 2.4}}}
person = 'Jeff Smith'
period = 'decades'
print("Hi my name is {name} and I'm {age[{0}]} {0} old.".format(period,**d[person]))

---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-95-ff05fa5df228> in <module>()
      1 period = 'decades'
----> 2 print('Hi my name is {name} and I\'m {age[{0}]} {0} old.'.format(period,**d[p]))

KeyError: '{0}'

[brennerm]

@agumonkey
Agree, I will add an array slicing example

[brennerm]

@bash-j
I don't really understand what you' re trying to accomplish, cause your code doesn't make sense to me.
What is your expected output?