How can I split a text file into multiple text files using python?
<p>I have a text file that contains the following contents. I want to split this file into multiple files (1.txt, 2.txt, 3.txt...). Each a new output file will be as the following. The code I tried doesn't split the input file properly. How can I split the input file into multiple files?</p>

<p><strong>My code:</strong></p>

<pre><code>#!/usr/bin/python

with open("input.txt", "r") as f:
    a1=[]
    a2=[]
    a3=[]
    for line in f:
        if not line.strip() or line.startswith('A') or line.startswith('$$'): continue
        row = line.split()
        a1.append(str(row[0]))
        a2.append(float(row[1]))
        a3.append(float(row[2]))
f = open('1.txt','a')
f = open('2.txt','a')
f = open('3.txt','a')
f.write(str(a1)) 
f.close()
</code></pre>

<p><strong>Input file:</strong></p>

<pre><code>A
x
k
..
$$

A
z
m
..
$$

A
B
l
..
$$
</code></pre>

<p><strong>Desired output 1.txt</strong></p>

<pre><code>A
x
k
..
$$
</code></pre>

<p><strong>Desired output 2.txt</strong></p>

<pre><code>A
z
m
..
$$
</code></pre>

<p><strong>Desired output 3.txt</strong></p>

<pre><code>A
B
l
..
$$
</code></pre>