recipie 0.0.3

Python idoms and recipes

Recipie

Python idoms and recipes

Submodule

Some recipie modules having the same name with standard libraries are meant as a drop in replacement for their counter parts. For example:

# Replace contextlib by recipie.contextlib

#from contextlib import *
from recipie.contextlib import *

# All standard contextlib and recipie.contextlib extensions are available

contextlib

cleanup(func, *args, **kwargs) [0.0.3]

Executes a clean up task on exiting context. The clean up task can be canceled.

Example:

with cleanup(undo, arg) as cleanup_task:
    result = action()
    if result:
        cleanup_task.cancel()

commit(func, *args, **kwargs) [0.0.1]

Executes func if the code ran to completion without any error:

Example:

def save_data(data):
    ...

with commit(save_data, data):
    # other actions
    ...

    # save_data is called if there is no error

• Also see rollback

rollback(func, *args, **kwargs) [0.0.1]

Executes func if when encouter error

Example:

def undo(data):
    ...

with rollback(undo, data):
    # Other actions
    ...

• Also see ***commit

Buffer [0.0.2]

Accumulates data into a buffer to be processed when the buffer is full.

Example:

def save_data(data: list[int]):
    ...

with Buffer(1000, save_data) as buffer:
    for i in range(1500):
        buffer.add(i)
        # On 1001th item, called save_data to save previous 1000 items
# When out of context, call save_data on the last 500 items

functools

@scoped [0.0.2]

"Namespaces are one honking great idea -- let's do more of those!"

Decorates a function to make it part of another namespace

Examples:

def retry():
    ...

# Put no_delay under "retry" so it can only be refered to as retry.no_delay
@scoped(retry)
def no_delay():
    ...

@default_on_error(value, errors) [0.0.1]

Decorates a function to return the specified value if errors is raised.

value: Default value to return on error

errors: Error or tuple of errors to check for

Example:

@default_on_error(None, KeyError)
def get_from_dict(dict_, key):
    return dict_[key] # Possible KeyError

value = get_from_dict(d, "Test") # Value is None when "Test" is not in d

@skip_on_error(errors) [0.0.1]

Decorates a function to return None if errors is raised (equivalent to @default_on_error(None, errors)

@retry(tries, errors, error_filter, delay_gen, log_error) [0.0.1]

Retries function tries times if encounter an error that matches errors and error_filter

tries: Number of attempts on the function. Must be at least 2

errors: exception or tuple of exception to retry

error_filter: function that takes in an error and returns True if it is a retriable error

delay_gen: Delay generator that produce an iterator of delay values for use between attempts. Example:

@retry(3, NetworkError) # Retry 3 times on NetworkError)
def get_db_connection():
   ...

conn = get_db_connection() # Automatically retry on network error

• Either errors or error_filter must be specified

Predefined delay policies:

1. retry.no_delay: No delay between attempts. This is picked up when no delay policy specified. It is equivalent to retry.const_delay(0).

2. retry.const_delay(delay): Delay in seconds as specified by delay

3. retry.expo_backoff(base, cap, jitter): exponential backoff delay. With no jitter, values are max(base * 2 ^ n, cap).

   • retry.no_jitter: (default) actual delay is fixed at the calculated value
   • retry.half_jitter: actual delay is randomly picked from [value/2, value)
   • retry.full_jitter: actual delay is randomly picked from [0, value)