This repo is a collection of the issues I faced when I started learning Flask.
It's meant to help beginners avoid the HELL of trying to solve problems at the start of learning a new framework.
Topics covered:
- Database connection
- SQLAlchemy
- Installation
- db.create_all()
- Data not updated
- MySQL
- Installation
- SQLAlchemy
- PDF generation
- WKHTMLTOPDF
- Installation
- Deployment
- PdfKit
- not rendering image
- WKHTMLTOPDF
- Runtime errors
- PermissionError: [Errno 13] Permission denied
- OSError: [Errno 48] Address already in use
- Jinja
Unfortiannely Jinja does not support global variables. The below example shows the issue:
{% set sum = 0 %}
{{ sum }} {# sum = 0 #}
{% for i in range(1,6) %}
{% set sum = sum + i %}
{% endfor %}
{{ sum }} {# sum = 0 instead of 15 #}There are two ways around this limitation:
- Using namespace (Added in version 2.10)
1.1 Example 1: summing numbers in a loop
1.2 Example 2: global flag
{% set global_var = namespace(sum=0) %} {{ global_var.sum }} {# sum = 0 #} {% for i in range(1,6) %} {% set global_var.sum = i + global_var.sum %} {% endfor %} {{ global_var.sum }} {# sum = 15 #}
{% set global_var = namespace(flag=false) %} {% for i in range(1,6) %} {% if i == 4 %} {% set global_var.flag=true %} {% endif %} {% endfor %} {% if global_var.flag %} 4 was found! {% endif %} {# Condition is true #}
Added in version 2.10
- Using global list
{% set global_list = [] %}
{{ global_list }} {# global_list = [] #}
{% for i in range(1,6) %}
{% if global_list.append(i) %}{% endif %}
{% endfor %}
{{ global_list }} {# global_list = [1, 2, 3, 4, 5] #}- YouTube channels
- Articles
