How to read data from txt file in python [duplicate]

Question

I have a names and numbers in my file (name of the file 'phone_book') and I tried to read all data using this code:

def read_phonebook():
    read = open("phone_book.txt", 'r')
    i = 0
    for i in (len(read)):
        print(i + '\t')

    read.close()

while True:
if menu == 2:
    read_phonebook()

but it gives Error: read_phonebook file has no len()

If I don't use len it keeps printing data because I'm using While loop. Could someone explain me how can I make this function to read list's whole data? with using While Loop?

docs.python.org/3/tutorial/… tells you all you need - it even comes with code examples... — Patrick Artner
– Patrick Artner, Commented Jun 2, 2018 at 17:23
Why are you using a while loop to read a file? What is menu? Why do you set i = 0 if the next command overwrites it? Why are you expecting len to give you an iterable? It would help you to make a minimal reproducible example. — wjandrea
– wjandrea, Commented Jun 2, 2018 at 17:52
If you wanted to loop over the length of anything, it would be for i in range(len(read)):... But read here is an iterable object, so using len() would actually iterate the entire thing before you printed each line, and you're left with a fully consumed iterable, meaning nothing can be printed after — OneCricketeer
– OneCricketeer, Commented Jun 2, 2018 at 19:58

everestial · Accepted Answer · 2018-06-02 19:45:35Z

4

Read the tutorials first.

if you are reading file defining a function isn't necessary.
learn basics first
if you are just reading file and you are a beginner in programming, you are taking a complicated approach.
take a simple approach and that helps you comprehend the input, output and ultimate goal.

Here is a quick tips for beginner and the simplest way of reading a file in python.

with open("phone_book.txt") as mytxt:
    for line in mytxt:
        print (line)

        Or do something with line

        # if you want to split the line
        # assuming data is tab separated
        newline = line.rstrip("\n").split("\t")

        # if you want conditional printing
        if len(line) > 0:
            print(line)

Lessons:

when you with open ... file will auto close at the end when it comes out of that scope.
using for line with out doing .read() prevents you from loading all the data on the memory.
fix your indentation issues

edited Jun 2, 2018 at 19:45

answered Jun 2, 2018 at 17:31

everestial

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2 Comments

Niklas R Over a year ago

Actually your indentation seems to be misaligned as well. :-P

everestial Over a year ago

Hmmmm, Good catch !

Rahul Goswami · Accepted Answer · 2018-06-02 17:25:12Z

0

Here, each line can be iterated on read.

def read_phonebook():
    read = open("phone_book.txt", 'r')
    i = 0
    for line in read:
        print(line)

    read.close()

answered Jun 2, 2018 at 17:25

Rahul Goswami

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