Quantopian's community platform is shutting down. Please read this post for more information and download your code.
Back to Community
Python Help: Sample Fundamentals 1 Algo
Dav
edited Mar 1, 2015

This code snippet is taken from the sample funadamental algo provided by Quantopian (https://www.quantopian.com/help#sample-live-trading).

# Find sectors with the highest average PE  
sector_pe_dict = {}  
for stock in fundamental_df:  
    sector = fundamental_df[stock]['morningstar_sector_code']  
    pe = fundamental_df[stock]['pe_ratio']

    if sector in sector_pe_dict:   # <----------------------- empty dictionary?  
        sector_pe_dict[sector].append(pe)  
    else:  
        sector_pe_dict[sector] = []

sector_pe_dict is initialized as an empty dictionary. In the for loop, the conditional stmt "if sector in sector_pe_dict" is testing an empty dictionary?

2 responses
Market Tech
Mar 1, 2015

@Dav, You've no doubt thought about your question a bit and now understand that yes, initially the dictionary is empty for the line you specify. And because it is empty the else clause will be executed.

else:  
    sector_pe_dict[sector] = []

Which mean that next time around, the dictionary will not be empty.

But more to the point, the test is looking for a specific key in its hash key list. Empty or not, if the hashkey is not found, the else: clause takes over. But if the hashkey, in this case a "sector" is found in the dictionary, rather than create a new array for that key (sector) the sector under test is appended to the array already found in the dictionary.

This is common code for all programming languages; testing for the existence of a key in a hash collection should be made part of your coding expertise.

Dav
Mar 1, 2015

Thanks Market Tech for the prompt and succinct reply. I was careless and failed to mentally trace the execution into the else clause. I'm new to Python but I'm gradually settling in. :)

About Quantopian
Careers
Community
Events
Documentation
Academia
Lectures
Status
Facebook
Twitter
LinkedIn
YouTube
Terms of Use
Privacy Policy

The material on this website is provided for informational purposes only and does not constitute an offer to sell, a solicitation to buy, or a recommendation or endorsement for any security or strategy, nor does it constitute an offer to provide investment advisory services by Quantopian.

In addition, the material offers no opinion with respect to the suitability of any security or specific investment. No information contained herein should be regarded as a suggestion to engage in or refrain from any investment-related course of action as none of Quantopian nor any of its affiliates is undertaking to provide investment advice, act as an adviser to any plan or entity subject to the Employee Retirement Income Security Act of 1974, as amended, individual retirement account or individual retirement annuity, or give advice in a fiduciary capacity with respect to the materials presented herein. If you are an individual retirement or other investor, contact your financial advisor or other fiduciary unrelated to Quantopian about whether any given investment idea, strategy, product or service described herein may be appropriate for your circumstances. All investments involve risk, including loss of principal. Quantopian makes no guarantees as to the accuracy or completeness of the views expressed in the website. The views are subject to change, and may have become unreliable for various reasons, including changes in market conditions or economic circumstances.