Иногда нужно выполнить блок кода с несколькими менеджерами контекста:
with open('f') as f: with open('g') as g: with open('h') as h: pass
Начиная с Python 2.7 и 3.1, это можно записать в одной конструкции with:
o = open with o('f') as f, o('g') as g, o('h') as h: pass
Раньше для этого использовали функцию contextlib.nested:
with nested(o('f'), o('g'), o('h')) as (f, g, h): pass
Если же число менеджеров контекста заранее неизвестно, лучше подойдёт более продвинутый инструмент. contextlib.ExitStack позволяет открывать любое число контекстов в произвольный момент, но гарантирует корректный выход из них в конце:
with ExitStack() as stack: f = stack.enter_context(o('f')) g = stack.enter_context(o('g')) other = [ stack.enter_context(o(filename)) for filename in filenames ]
Иногда нужно выполнить блок кода с несколькими менеджерами контекста:
with open('f') as f: with open('g') as g: with open('h') as h: pass
Начиная с Python 2.7 и 3.1, это можно записать в одной конструкции with:
o = open with o('f') as f, o('g') as g, o('h') as h: pass
Раньше для этого использовали функцию contextlib.nested:
with nested(o('f'), o('g'), o('h')) as (f, g, h): pass
Если же число менеджеров контекста заранее неизвестно, лучше подойдёт более продвинутый инструмент. contextlib.ExitStack позволяет открывать любое число контекстов в произвольный момент, но гарантирует корректный выход из них в конце:
with ExitStack() as stack: f = stack.enter_context(o('f')) g = stack.enter_context(o('g')) other = [ stack.enter_context(o(filename)) for filename in filenames ]
Bitcoin is built on a distributed digital record called a blockchain. As the name implies, blockchain is a linked body of data, made up of units called blocks that contain information about each and every transaction, including date and time, total value, buyer and seller, and a unique identifying code for each exchange. Entries are strung together in chronological order, creating a digital chain of blocks. “Once a block is added to the blockchain, it becomes accessible to anyone who wishes to view it, acting as a public ledger of cryptocurrency transactions,” says Stacey Harris, consultant for Pelicoin, a network of cryptocurrency ATMs. Blockchain is decentralized, which means it’s not controlled by any one organization. “It’s like a Google Doc that anyone can work on,” says Buchi Okoro, CEO and co-founder of African cryptocurrency exchange Quidax. “Nobody owns it, but anyone who has a link can contribute to it. And as different people update it, your copy also gets updated.”
