How do I read a random character from a plain text file

Question

I do not know how to read a random character from a text file, and would like to learn how.

This is what happened when I started messing around with python! I know I will be doing something like this later on in school so I am practising. Reading a line would not suffice as you will see - I am open to tips and just a straight answer as I realise my code is very sloppy. The Raspberry Pi with this code on is running Raspbian lite with a few bits extra installed (a gui, idle), and runs python 3.5.3.

I write some of these to a text file:

f = open("selected.txt","w")
chars = 'abcdefghijklmnopqrstuvwxyz'
ucchars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
smbls = '`¬!"£$%^&*()-_=+{[}]:;@~#<,>.?'
nos = '1234567890'
space = ' '

Like this:

usechars = input('Use lower case letters? answer y or n.')
if usechars == 'y':
    f.write(chars)
useucchars = input('Use upper case letters? answer y or n.')
if useucchars == 'y':
    f.write(ucchars)
usesmbls = input('Use symbols? answer y or n.')
if usesmbls == 'y':
    f.write(smbls)
usenos = input('Use numbers 0-9? answer y or n.')
if usenos == 'y':
    f.write(nos)
usespace = input('Use spaces? answer y or n.')
if usespace == 'y':
    f.write(space)

I would like to print a selected amount of random characters from the text file and print it in the shell, but I do not know how to get a random single character from a text file. If there would be a better way of doing it (probably the case) or you need more code please tell me. Thanks in advance.

UPDATE here is the code:

f.close()
with open("selected.txt","r") as f:
    contents = f.read
random_character = random.choice(contents)
for i in range(amnt):
    password = ''
    for c in range(length):
        password += random_character
    print(password)

Your updated code contains several errors which I address in my update to my answer. You might also want to check the StackOverflow docs on [what do to with answers](https://stackoverflow.com/help/someone-answers). — chthonicdaemon, Apr 09 '19 at 17:37

chthonicdaemon · Accepted Answer · 2019-04-09T17:36:05.513

1

If the file is not very large an easy way to pick a random character is to read it into a string first, then just select a random character from the string:

import random

with open("selected.txt", "r") as f:
    contents = f.read()  # NOTE the () after read

random_character = random.choice(contents)
print("The random character I've chosen is: ", random_character)

If you'd like to create a string with random choices you can use your for loop, but you have to choose a new random character inside the loop:

with open("selected.txt","r") as f:
    contents = f.read()

password = ''
for i in range(amnt):
    random_character = random.choice(contents)
    for c in range(length):
        password += random_character
print(password)

edited Apr 09 '19 at 17:36

answered Apr 09 '19 at 15:17

chthonicdaemon

19,180
2
52
66

I am getting an error message. It is probably my bare bones installation of python but it could be my code ```Traceback (most recent call last): File "/home/pi/password.py", line 33, in random_character = random.choice(contents) File "/usr/lib/python3.5/random.py", line 262, in choice i = self._randbelow(len(seq)) TypeError: object of type 'builtin_function_or_method' has no len()``` – Jeremy Apr 09 '19 at 15:33
2

I suspect you have `f.read` instead of `f.read()` (with the parens) in your code. – chthonicdaemon Apr 09 '19 at 16:16
Indeed, that can be seen on line 2 of the last block of code in the OP. – bart cubrich Apr 09 '19 at 16:35

How do I read a random character from a plain text file

1 Answers1