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# Makes sure that code is cleaned up after the execution of the body, no matter what the body contains.

class controlled_execution:
	def __enter__(self):
		# set things up, e.g. open file
		return thing   # e.g. file itself
    def __exit__(self, type, value, traceback):
        # tear things down, e.g. close file

with controlled_execution() as thing:
	# some code, e.g. write to file

# a = append / r = read / w = write / x = exclusive creation, fails if file exists.
with open('file.txt', 'a') as out:   
	out.write(var + '/n')

#!/usr/bin/env python
#!/usr/bin/env python3

# Importing from another file/module: Place __init__.py in same folder.
import my_file
from my_file import class_or_function_name

if __name__ == "__main__":
	main()

[1 if a>b else 0 for a,b in zip(arr_a, arr_b)]  # if a>b else 0 = expression
[1 for a,b in zip(arr_a, arr_b) if a>b]         # if a>b = filter

# Initializing from list
keys = ['one', 'two', 'three']
d = {key: 0 for key in keys}

# Iterating
for key in d:
for key in d.keys():
for val in d.values():
for key, value in d.items():

for key, value in d.iteritems():	# Python 2

# d.items() or d.keys() in Python 2 are not dynamic:
>>> d = { "first" : 1, "second" : 2 }
>>> ks = d.keys()
>>> d["third"] = 3
>>> ks
['second', 'first']