pandas calculate return by shifting timeseries index

 usually, we calculate the return with next row data by simply using df.Close.shift()

but if we want shifting by a specific time period, can try:

df['ret15min'] = (df.Close.shift(-15, freq="min") -df.Close)*100/df.Close

Install without root access / for current user

 You can use conda to install mysql client!

https://stackoverflow.com/questions/36651091/how-to-install-packages-in-linux-centos-without-root-user-with-automatic-depen/52561058#52561058

recreate / cloning conda env with limited internet access

• https://www.anaconda.com/blog/moving-conda-environments
• https://docs.conda.io/projects/conda/en/latest/user-guide/tasks/manage-environments.html

Generate FPS QR Code with customized amount

1. Scan an existing QR code at https://zxing.org/w/decode.jspx to get the text content
2. Remove the last 4 characters, which is the checksum (CRC), from the text content
3. Spot the substring that contains the amount from the text content
4. Replace the amount substring with new amount using the *same number* of characters, for example, replacing 
• 1755.00
• with
• 0050.00
• will update the amount from $1,755 to $50
5. Calculate the new checksum
1. http://www.sunshine2k.de/coding/javascript/crc/crc_js.html
1. width: CRC-16
2. parametrization: Custom
3. Polynomial: 0x1021
4. Initial Value: 0xFFFF
5. Input Data: String
6. Paste the updated text content from above
7. Click Calculate CRC
6. Generate new QR code
1. https://www.qrcode-monkey.com/#text
2. Paste the updated text content appended with the new 4-character CRC
3. Click Create QR Code

Ref: FPS QR code specification at https://www.hkma.gov.hk/media/eng/doc/key-functions/financial-infrastructure/infrastructure/retail-payment-initiatives/Common_QR_Code_Specification.pdf

send email html content with inline image

• preferred way:
• script to generate html content with image encoded as base64 text
• <img src='data:imag/png;base64,....'/>
• base64.b64encode().decode("ascii") to get that ... string from image
• single html file to include all the html and images, etc. 😀
• cat that html and pipe to mutt -e "set content_type=text/html" to send the email

• however, outlook does not support inline base64 image 😞
• one way to workaround is to pipe the html to a python script that
• extract that base64 string (... above)
• replace html code with <img src='cid:123' />
• create image object with
• image = MIMEImage(base64.decodebytes(....encode("ascii")), _subtype=<png/jpg/etc>)
• reference this image by
• image.add_header('Content-ID', '<123>')
• send the emails as shown in this example
• https://docs.python.org/3/library/email.examples.html
• To send from windows outlook client rather than directly via smtp server:
• https://stackoverflow.com/questions/44544369/i-am-not-able-to-add-an-image-in-email-body-using-python-i-am-able-to-add-a-pi

url to pdf on linux

yum install wkhtmltopdf
To manipulate the pdfs, use pdfunite / pdfseparate from
yum install poppler-utils

centos minimal

install centos 8 minimal

install google-chrome from google repo, which should install all the X dependencies

additional language support for web page display

> yum groupinstall Fonts

To start chrome full screen
> X& DISPLAY=:0 google-chrome --window-size=1920,1080&

if sound is not already working,
> yum install alsa-utils
unmute everything with
> alsamixer
https://wiki.archlinux.org/index.php/Advanced_Linux_Sound_Architecture#Disabling_auto_mute_on_startup