- generators.py
- generators.py
#!# ============
#!# Generators
#!# ============
#!#
#!# This page contains a memo on generators.
#!#
#!# For a complete reference documentation, look at
#!# https://docs.python.org/3/reference/expressions.html#generator-expressions
####################################################################################################
from Tools import *
import asyncio
####################################################################################################
#!# List Comprehensions
#!# -------------------
a_list = [x for x in range(10)]
print(a_list)
#o#
a_set = {x % 10 for x in range(100)}
print(a_set)
#o#
a_dict = {x:x for x in range(5)}
print(a_dict)
#o#
#!# Nested List Comprehensions
#!# ~~~~~~~~~~~~~~~~~~~~~~~~~~
a_list_of_list = [[x, y]
for x in range(2)
for y in range(4)]
print(a_list_of_list)
#o#
#!# Filtered List Comprehensions
#!# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
a_list = [x for x in range(10)
if 2 <= x <= 6]
print(a_list)
#o#
a_list_of_list = [[x, y]
for x in range(10)
for y in range(10)
if 2 <= x <= 3 and 5 <= y <= 6]
print(a_list_of_list)
#o#
####################################################################################################
#!# Generator expressions
#!# ---------------------
N = 4
multiplication_table = (x*y for x in range(1, N+1) for y in range(1, N+1))
print(list(multiplication_table))
#o#
#!# Yield expressions
#!# -----------------
def simplist_generator():
yield 1
print(list(simplist_generator()))
#o#
def range_clone(N):
for i in range(N):
yield i
print(list(range_clone(10)))
#o#
#!# A generator exit when :code:`StopIteration` is raised:
def generator(N, M):
value = N
while True:
yield value
value += 1
if M <= value:
raise StopIteration
print(list(generator(10, 20)))
#o#
#!# We can yield from a generator instead of a value:
def generator(N):
yield from range_clone(N)
print(list(generator(10)))
#o#
#!# Generator-iterator Methods
#!# --------------------------
def echo(value=None):
print("echo is running")
try:
while True:
try:
value = (yield value)
except Exception as exception:
print('exception:', exception)
value = exception
finally:
# cleanup code
print("reached finally")
generator = echo(1)
#o#
#!# Starts the execution of a generator function or resumes it at the last executed yield expression.
print(next(generator))
#o#
print(next(generator))
#o#
#!# Resumes the execution and “sends” a value into the generator function.
print(generator.send(2))
#o#
#!# Raises an exception of type type at the point where the generator was paused.
# generator.throw(type[, value[, traceback]])
generator.throw(TypeError, "spam")
#o#
#!# Raises a :code:`GeneratorExit` at the point where the generator function was paused.
generator.close()
#o#
#!# Asynchronous Generator Functions
#!# --------------------------------
#!# **To be completed**
#!#
#!# For further information see `PEP 525 -- Asynchronous Generators <https://www.python.org/dev/peps/pep-0525>`_
async def ticker(delay, to):
"""Yield numbers from 0 to `to` every `delay` seconds."""
for i in range(to):
yield i
await asyncio.sleep(delay)
#!# Asynchronous Generator-Iterator Methods
#!# ---------------------------------------
#!# **To be completed**
3.3.8. Generators¶
This page contains a memo on generators.
For a complete reference documentation, look at https://docs.python.org/3/reference/expressions.html#generator-expressions
from Tools import *
import asyncio
3.3.8.1. List Comprehensions¶
a_list = [x for x in range(10)]
print(a_list)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
a_set = {x % 10 for x in range(100)}
print(a_set)
{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
a_dict = {x:x for x in range(5)}
print(a_dict)
{0: 0, 1: 1, 2: 2, 3: 3, 4: 4}
3.3.8.1.1. Nested List Comprehensions¶
a_list_of_list = [[x, y]
for x in range(2)
for y in range(4)]
print(a_list_of_list)
[[0, 0], [0, 1], [0, 2], [0, 3], [1, 0], [1, 1], [1, 2], [1, 3]]
3.3.8.1.2. Filtered List Comprehensions¶
a_list = [x for x in range(10)
if 2 <= x <= 6]
print(a_list)
[2, 3, 4, 5, 6]
a_list_of_list = [[x, y]
for x in range(10)
for y in range(10)
if 2 <= x <= 3 and 5 <= y <= 6]
print(a_list_of_list)
[[2, 5], [2, 6], [3, 5], [3, 6]]
3.3.8.2. Generator expressions¶
N = 4
multiplication_table = (x*y for x in range(1, N+1) for y in range(1, N+1))
print(list(multiplication_table))
[1, 2, 3, 4, 2, 4, 6, 8, 3, 6, 9, 12, 4, 8, 12, 16]
3.3.8.3. Yield expressions¶
def simplist_generator():
yield 1
print(list(simplist_generator()))
[1]
def range_clone(N):
for i in range(N):
yield i
print(list(range_clone(10)))
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
A generator exit when StopIteration is raised:
def generator(N, M):
value = N
while True:
yield value
value += 1
if M <= value:
raise StopIteration
print(list(generator(10, 20)))
[10, 11, 12, 13, 14, 15, 16, 17, 18, 19]
/home/opt/python-virtual-env/py36/lib/python3.6/site-packages/ipykernel_launcher.py:9: DeprecationWarning: generator 'generator' raised StopIteration
if __name__ == '__main__':
We can yield from a generator instead of a value:
def generator(N):
yield from range_clone(N)
print(list(generator(10)))
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
3.3.8.4. Generator-iterator Methods¶
def echo(value=None):
print("echo is running")
try:
while True:
try:
value = (yield value)
except Exception as exception:
print('exception:', exception)
value = exception
finally:
# cleanup code
print("reached finally")
generator = echo(1)
Starts the execution of a generator function or resumes it at the last executed yield expression.
print(next(generator))
echo is running
1
print(next(generator))
None
Resumes the execution and “sends” a value into the generator function.
print(generator.send(2))
2
Raises an exception of type type at the point where the generator was paused.
# generator.throw(type[, value[, traceback]])
generator.throw(TypeError, "spam")
exception: spam
Raises a GeneratorExit at the point where the generator function was paused.
generator.close()
reached finally
3.3.8.5. Asynchronous Generator Functions¶
To be completed
For further information see PEP 525 – Asynchronous Generators
async def ticker(delay, to):
"""Yield numbers from 0 to `to` every `delay` seconds."""
for i in range(to):
yield i
await asyncio.sleep(delay)
3.3.8.6. Asynchronous Generator-Iterator Methods¶
To be completed