Loops and Conditionals

Planners are repetitive by nature - twelve month pages, up to 31 day pages per month, seven weekday headers in every table. Loops let you generate all that HTML from a single block of code. Conditionals let you change what appears based on the data - for example highlighting weekends in red.

Key topics

for loops and how to iterate over months, days, weeks.
The loop helper variable (index, first, last).
if / elif / else conditionals.
The is none test for empty calendar cells.

For loops

A for loop repeats a block of HTML once for every item in a list.

Template:

<ul>
  %% for month in year.months
  <li>{{ month }}</li>
  %% endfor
</ul>

Output:

<ul>
  <li>January</li>
  <li>February</li>
  <li>March</li>
  <li>April</li>
  <li>May</li>
  <li>June</li>
  <li>July</li>
  <li>August</li>
  <li>September</li>
  <li>October</li>
  <li>November</li>
  <li>December</li>
</ul>

year.months is a list of twelve Month objects. On each pass through the loop the variable month holds the current item. The name before in is up to you - month, m or anything else.

Nested loops

Loops can be placed inside other loops. The planner template uses this to build calendar tables - an outer loop over weeks and an inner loop over days in each week.

Template:

%% for month in year.months
<h2>{{ month }}</h2>
<table>
  %% for week in month.table
  <tr>
    %% for day in week
    <td>{{ day }}</td>
    %% endfor
  </tr>
  %% endfor
</table>
%% endfor

Output (January 2026 excerpt, first two weeks):

<h2>January</h2>
<table>
  <tr>
    <td></td>
    <td></td>
    <td></td>
    <td>1</td>
    <td>2</td>
    <td>3</td>
    <td>4</td>
  </tr>
  <tr>
    <td>5</td>
    <td>6</td>
    <td>7</td>
    <td>8</td>
    <td>9</td>
    <td>10</td>
    <td>11</td>
  </tr>
  ...
</table>

Some cells are empty because January 2026 starts on a Thursday. We will handle those empty cells with a conditional below.

The `loop` variable

Inside every for block Jinja2 provides a special variable called loop with useful information about the current iteration.

Property	Description
`loop.index`	Current iteration, starting at 1.
`loop.index0`	Current iteration, starting at 0.
`loop.first`	`true` on the first iteration.
`loop.last`	`true` on the last iteration.
`loop.length`	Total number of items.

Template:

<ul>
  %% for month in year.months
  <li>{{ loop.index }}. {{ month }}</li>
  %% endfor
</ul>

Output:

<ul>
  <li>1. January</li>
  <li>2. February</li>
  <li>3. March</li>
  ...
  <li>12. December</li>
</ul>

Using `loop.index0` for tuple access

When a planner has twelve month pages, each with its own background image, the images can be stored in a tuple and accessed by position using loop.index0:

Template:

%% set month_backgrounds = (
  "assets/jan.png",
  "assets/feb.png",
  "assets/mar.png",
)

%% for month in year.months
<div class="page">
  <img class="back" src="{{ base }}/{{ month_backgrounds[loop.index0] }}">
  <h2>{{ month }}</h2>
</div>
%% endfor

On the first iteration loop.index0 is 0, so it picks assets/jan.png. On the second it is 1, and so on.

Tip

Use loop.index0 (zero-based) when indexing into a list or tuple. Use loop.index (one-based) when displaying a number to the reader.

If / elif / else

Conditionals let you show or hide HTML based on a condition.

Template:

%% for day in calendar.weekdays
%% if day.is_off_day
<th style="color: red;">{{ day.short_name }}</th>
%% else
<th>{{ day.short_name }}</th>
%% endif
%% endfor

Output:

<th>Mon</th>
<th>Tue</th>
<th>Wed</th>
<th>Thu</th>
<th>Fri</th>
<th style="color: red;">Sat</th>
<th style="color: red;">Sun</th>

Saturday and Sunday have is_off_day set to true, so they get the red style.

Inline conditionals

For short checks you can write the condition on one line:

<th{{ ' style="color: red;"' if day.is_off_day else '' }}>
  {{ day.short_name }}
</th>

This produces the same result as the block form above but is more compact.

The `is none` test

month.table is a grid of weeks and days. Some cells are empty - for example January 2026 starts on Thursday, so Monday through Wednesday of the first week have no day. These cells contain None.

Use is none (or is not none) to check:

Template:

%% for week in month.table
<tr>
  %% for day in week
  %% if day is not none
  <td>{{ day }}</td>
  %% else
  <td></td>
  %% endif
  %% endfor
</tr>
%% endfor

Output (January 2026, first week):

<tr>
  <td></td>
  <td></td>
  <td></td>
  <td>1</td>
  <td>2</td>
  <td>3</td>
  <td>4</td>
</tr>

Warning

Always use is none or is not none instead of == None or != None. The is form is the correct Jinja2 way.

Do:

%% if day is not none

Don’t:

%% if day != None

Do and don’t summary

Do	Don’t
`%% if day is not none`	`%% if day != None`
`loop.index0` for tuple/list access.	`loop.index` when you need zero-based indexing.
Close every `for` with `endfor`.	Forget `%% endfor` - the template will fail to render.
Close every `if` with `endif`.	Forget `%% endif`.

Update the Demo Planner

Add a second page that shows a calendar table for the month. Open planners/demo/demo.html and add the following after the cover page div (before </body>):

<div class="page" id="{{ month.id }}">
  <img class="back" src="{{ base }}/assets/calendar.png">
  <h2 style="text-align: center; margin-top: 15mm;
             font-size: 22pt; letter-spacing: 5mm;">
    {{ month }}
  </h2>
  <p style="text-align: center; font-size: 14pt;">
    {{ year }}
  </p>
  <table style="width: calc(100% - 10mm);
                margin: 10mm 5mm 0 5mm;
                border-collapse: collapse;
                font-size: 14pt; text-align: center;
                table-layout: fixed;">
    <thead>
      <tr>
        %% for wd in calendar.weekdays
        %% if wd.is_off_day
        <th style="color: #C00000;">{{ wd.short_name }}</th>
        %% else
        <th>{{ wd.short_name }}</th>
        %% endif
        %% endfor
      </tr>
    </thead>
    <tbody>
      %% for week in month.table
      <tr>
        %% for day in week
        %% if day is not none
        <td>{{ day }}</td>
        %% else
        <td></td>
        %% endif
        %% endfor
      </tr>
      %% endfor
    </tbody>
  </table>
</div>

This uses three nested concepts you learned on this page:

A loop over calendar.weekdays for the header row.
A conditional to color weekends red.
Nested loops over month.table (weeks, then days) with an is not none check for empty cells.

Regenerate:

pyplanner planners/demo

You should now see two pages - the cover and a month calendar.

What is next

The calendar table has quite a lot of repeated HTML. Continue to Macros to extract it into a reusable macro.

Loops and Conditionals

For loops

Nested loops

The loop variable

Using loop.index0 for tuple access

If / elif / else

Inline conditionals

The is none test

Do and don’t summary

Update the Demo Planner

What is next

The `loop` variable

Using `loop.index0` for tuple access

The `is none` test