CODEWITHSUNDEEP
pythonprintinglines
Robbie
Robbie

Reputation: 61

How do I only print every 5th line

I have a text file ("name_data.txt") that has the following contents:

name: Kelo
family name: Lam
location: Asia
members: Kelo, Kiko, Jil

name: Miko
family name: Naiton
location: Japan
members: Miko,Kayati

The text file keeps going with the same pattern (name, family name, location, members)

I want to print out the first line and then print every 5th line so I would be printing only the line with "name" in the beginning. I then want to have a list of the names

I want my output to be :

["Kelo","Miko"]

So far, I have gotten (although, it is wrong):

name_data= load_local_file('name_data.txt',ignore_header=False,delimiter='\t')


def __init __(name_reader): 

    names=list()  
    count=0  
    name_line=5  
    line_number=0  

    for name in name_data:

        if line_number<5:  

            line_number +=1  

        if line_number ==5: 

            names.append(line_number)

Upvotes: 6

Views: 2402

Answers (6)

quapka
quapka

Reputation: 2929

You can use regular expressions - Python's module for that is re.

Then with name_data.txt being:

name: Kelo
family name: Lam
location: Asia
members: Kelo, Kiko, Jil

name: Miko
family name: Naiton
location: Japan
members: Miko,Kayati

Getting the names is simple one-liner:

import re

def get_names():

    with open('name_data.txt', 'r') as f:
        print(re.findall(r'^name:\s*(\w+)', f.read(), flags=re.MULTILINE))

if __name__ == '__main__':

    get_names()

Note the multiline flag setting - when the setting is global, the regex would also match lines with family name: .... See the regex in interactive mode here.

Upvotes: 0

MSeifert
MSeifert

Reputation: 152647

You can identify every fifth line by comparing the linenumber modulo 5 against a number. In your case this should be 0 because you want the first line and the 6th, the 11th, ... (note that python starts with index 0)

To get the line-numbers as well as the content you can iterate over the file with enumerate.

Then to discard the name: part of the string and keep what comes after, you can use str.split().

A working implementation could look like this:

# Create an empty list for the names
names = []

# Opening the file with "with" makes sure it is automatically closed even
# if the program encounters an Exception.
with open('name_data.txt', 'r') as file:
    for lineno, line in enumerate(file):
        # The lineno modulo 5 is zero for the first line and every fifth line thereafter.
        if lineno % 5 == 0:
            # Make sure it really starts with "name"
            if not line.startswith('name'):
                raise ValueError('line did not start with "name".')
            # Split the line by the ":" and keep only what is coming after it.
            # Using `maxsplit=1` makes sure you don't run into trouble if the name 
            # contains ":" as well (may be unnecessary but better safe than sorry!)
            name = line.split(':', 1)[1]
            # Remove any remaining whitespaces around the name
            name = name.strip()
            # Save the name in the list of names
            names.append(name)

# print out the list of names
print(names)

Instead of enumerate you could also use itertools.islice with a step argument:

from itertools import islice

with open('name_data.txt', 'r') as file:
    for line in islice(file, None, None, 5):
        ... # like above except for the "if lineno % 5 == 0:" line

Depending on your needs you might consider using the re module to completly parse the file:

import re
# The regular expression
group = re.compile(r"name: (.+)\nfamily name: (.+)\nlocation: (.+)\nmembers: (.+)\n", flags=re.MULTILINE)
with open(filename, 'r') as file:
    # Apply the regex to your file
    all_data = re.findall(group, file)
# To get the names you just need the first element in each group:
firstnames = [item[0] for item in all_data]

The firstnames will be ['Kelo', 'Miko'] for your example and similar if you use [item[1] for item in all_data] then you get the last names: ['Lam', 'Naiton']. To successfully use a regular expression you must ensure it really matches your file layout otherwise you'll get wrong results.

Upvotes: 4

Ramon Zuniga
Ramon Zuniga

Reputation: 355

Having a name_data.txt file with data as follows: 1 2 3 4 5 6 7 8 9 10

Here's how you can print the first and every 5th line of it:

content = [line.rstrip('\n') for line in open('name_data.txt')]
names = []
limit = 4
fp = open("name_data.txt")
names.append(content[0])
for i, line in enumerate(fp):
    if i == limit:
        names.append(line)
        limit += 5
fp.close()
print(names)

Checkout http://shortcode.pro/code/read-txt-file-and-print-first-and-every-5th-line/

Upvotes: 0

Tom
Tom

Reputation: 1686

A simple way to do this would be as follows:

with open('name_data.txt', 'r') as file:

    index = 0
    for line in file:
        if index % 5 == 0:
            print(line.split()[1])
        index += 1

Upvotes: 2

datawrestler
datawrestler

Reputation: 1567

You could do this in one line with a list comprehension 

c = open('test.txt', 'r').readlines()

# for every fifth line extract out name and store in list
a = [i.replace('name: ', '').replace('\n', '') for i in c[::5]]

print(a) # ['Kelo', 'Miko']

Upvotes: 2

Iluvatar
Iluvatar

Reputation: 1537

Assuming that name_data is a list of lines in the file, you can do

names = []
for i in range(1, len(name_data), 5):
    names.append(name_data[i].split(":")[1].strip())

Upvotes: 1

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