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Robb Shecter dogweather

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dogweather / breadcrumbs.rb
Created Sep 4, 2020
Breadcrumbs, OO version
View breadcrumbs.rb
# typed: false
# frozen_string_literal: true
require 'json'
module PublicLaw
# Represents a breadcrumb trail on a page.
class Breadcrumbs
include ActionView::Helpers
extend T::Sig
View de_dup_adjacents.rb
# Remove adjacent duplicates in an array.
# @param [Array] a_list the array to de-dup
# @return [Array] the processed list of items
# @note Created to help display a user's log entries.
def de_dup(a_list)
a_list.reduce([]) do |new_list, elem|
new_list + (new_list.last.eql?(elem) ? [] : [elem])

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Introduction to Lists

We just talked about Python's basic data types, string, integer and floating point objects. Python variables, then are like labels for objects; they're a way to refer to them.

But when writing real programs, one soon wishes there was more. For example, when there are lots of objects, which pretty much every program has. This gets tedious fast:

# Pull the category back out of the meta dict.
parent_category = response.meta["category"]
# Create a new items.Brand with the scraped data.
# ...
# Add the new brand to its parent in the tree.
# Create a new Category to hold the scraped info. Also,
# prepare it for holding its brands.
category = items.Category(number="...", name="...", url="...", brands=[])
# Save the category into the tree structure.
# Create a request for the Category's page, which
# will list all its Brands.
# Pass the Category Item in the meta dict.
def __init__(self):
# A flag, set after post-processing is finished, to
# avoid an infinite loop.
self.data_submitted = False
# The object to return for conversion to a JSON tree.
# All the parse methods add their results to this
# structure.
View json-fragment.json
"categories": [
"kind": "Category",
"number": "101",
"name": "Skateboards",
"url": "",
"brands": [
"kind": "Brand",
def from_crawler(cls, crawler, *args, **kwargs):
"""Register to receive the idle event"""
spider = super(SecureSosStateOrUsSpider, cls).from_crawler(
crawler, *args, **kwargs
crawler.signals.connect(spider.spider_idle, signal=signals.spider_idle)
return spider
def spider_idle(self, spider):
View lesson-zero.ipynb
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