A simple implementation of the Promise specification. See: https://promisesaplus.com Promise is in essence a syntactic sugar for callbacks. Simplifies passing values from functions that might do work in asynchronous manner. Example usage: * Passing return value of one funct
| 14 | |
| 15 | |
| 16 | class Promise(object): |
| 17 | """A simple implementation of the Promise specification. |
| 18 | |
| 19 | See: https://promisesaplus.com |
| 20 | |
| 21 | Promise is in essence a syntactic sugar for callbacks. Simplifies passing |
| 22 | values from functions that might do work in asynchronous manner. |
| 23 | |
| 24 | Example usage: |
| 25 | |
| 26 | * Passing return value of one function to another: |
| 27 | |
| 28 | def do_work_async(resolve): |
| 29 | # "resolve" is a function that, when called with a value, resolves |
| 30 | # the promise with provided value and passes the value to the next |
| 31 | # chained promise. |
| 32 | resolve(111) # Can be invoked asynchronously. |
| 33 | |
| 34 | def process_value(value): |
| 35 | assert value === 111 |
| 36 | |
| 37 | Promise(do_work_async).then(process_value) |
| 38 | |
| 39 | * Returning Promise from chained promise: |
| 40 | |
| 41 | def do_work_async_1(resolve): |
| 42 | # Compute value asynchronously. |
| 43 | resolve(111) |
| 44 | |
| 45 | def do_work_async_2(resolve): |
| 46 | # Compute value asynchronously. |
| 47 | resolve(222) |
| 48 | |
| 49 | def do_more_work_async(value): |
| 50 | # Do more work with the value asynchronously. For the sake of this |
| 51 | # example, we don't use 'value' for anything. |
| 52 | assert value === 111 |
| 53 | return Promise(do_work_async_2) |
| 54 | |
| 55 | def process_value(value): |
| 56 | assert value === 222 |
| 57 | |
| 58 | Promise(do_work_async_1).then(do_more_work_async).then(process_value) |
| 59 | """ |
| 60 | |
| 61 | def __init__(self, executor): |
| 62 | """Initialize Promise object. |
| 63 | |
| 64 | Arguments: |
| 65 | executor: A function that is executed immediately by this Promise. |
| 66 | It gets passed a "resolve" function. The "resolve" function, when |
| 67 | called, resolves the Promise with the value passed to it. |
| 68 | """ |
| 69 | self.value = None |
| 70 | self.resolved = False |
| 71 | self.mutex = threading.Lock() |
| 72 | self.callbacks = [] |
| 73 | self._invoke_executor(executor) |
no outgoing calls