All control statements are placed in {%… %}, and there is a statement {% endxxx %} to end, the commonly used control statements in Jinja are if/for…in…
1. Condition control: if statement
- The if statement is similar to that in python, you can use >, <, <=, >=, ==, != to make judgments, and you can also use and, or, not, () to perform logical merging operations
from flask import Flask,render_template
app=Flask(__name__)
context={
'username': '老萝卜'
}
@app.route("/")
def if_for():
return render_template('demo_flaskif.html', **context)
if __name__=="__main__":
app.run(debug=True)
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Flask if控制语句演示</title>
</head>
<body>
{
%if username=="老萝卜"%}
<p>当前用户是：{
{
username}}</p>
{
%else%}
<p>当前用户不是：老萝卜,而是{
{
username}}</p>
{
%endif%}
</body>
</html>
Change username to another value,'username':'laoluobo'
2. Loop control: for...in...
- The for loop can traverse any sequence including lists, dictionaries, and tuples. And can be reverse traversed
- If there is no value in the sequence, enter else
- And the for loop in Jinja also contains the following variables, which can be used to get the current traversal status
| variable | description |
|---|---|
| loop.index | The index of the current iteration (starting from 1) |
| loop.index0 | The index of the current iteration (starting from 0) |
| loop.first | Whether it is the first iteration, return True or False |
| loop.last | Whether it is the last iteration, return True or False |
| loop.length | The length of the sequence |
- In addition, you cannot use continue and break expressions to control the execution of the loop.
from flask import Flask,render_template
app=Flask(__name__)
context={
'books': ['Python', 'Java', 'PHP'],
'book': {
'Python': 666,
'Java': 777,
'PHP': 888
},
"netebooks":[]
}
@app.route("/")
def flask_for():
return render_template('demo_flaskfor.html', **context)
if __name__=="__main__":
app.run(debug=True)
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Flask if控制语句演示</title>
</head>
<body>
<p> 循环显示列表 books：</p>
{
% for book in books %} <!--循环显示列表-->
<p>{
{
book }}</p>
{
% else %}
<p>列表books为空列表</p>
{
% endfor %}
<hr>
<p> 循环显示列表 notebooks：</p>
{
% for book in notebooks %} <!--循环显示空列表-->
<p>{
{
book }}</p>
{
% else %}
<p>列表notebooks为空列表</p>
{
% endfor %}
<hr>
<p>循环显示字典：</p>
{
% for i in book %} <!--循环显示字典-->
<p>{
{
i }}</p>
{
% endfor %}
<hr>
<p>循环显示字典的key和value</p>
{
% for key, value in book.items() %} <!--循环显示字典的key和value -->
<p>{
{
key }} -- {
{
value }}</p>
{
% endfor %}
<hr>
<p>显示循环当前遍历状态 </p>
{
% for book in books %}
<p>{
{
book }}</p>
<p>当前迭代的索引（从0开始）：{
{
loop.index0 }}</p>
{
% if loop.first %}
<p>是否是第一次迭代，返回True或False：{
{
loop.first }}</p>
{
% endif %}
{
% if loop.last %}
<p>是否是最后一次迭代，返回True或False：{
{
loop.last }}</p>
{
%endif%}
{
% endfor %}
</body>
</html>
