Python Print First N Lines of String

python print first n lines of string

If you only want to get the 10 first elements of the list then just slice the list accordingly

for word, numbers in enumerate(sorted[:10]):
        print(word,':',numbers)

How to print the first n lines of file?

Literally, read first n lines, then stop.

def read_first_lines(filename, limit):
  result = []
  with open(filename, 'r') as input_file:
    # files are iterable, you can have a for-loop over a file.
    for line_number, line in enumerate(input_file):
      if line_number > limit:  # line_number starts at 0.
        break
      result.append(line)
  return result

Python how to get last N lines of a multiline string

str.splitlines() with a simple slice:

mstr.splitlines()[-n:]

The solution above will return these lines as a list. If you want a string, you also need to use str.join():

'\n'.join(mstr.splitlines()[-n:])

If your text doesn't contain it, you might also want to add the last newline, if you're catenating it with other text, or writing it to a file on UNIX-like OS:

'\n'.join(mstr.splitlines()[-n:]) + '\n'

How to read first N lines of a file?

Python 3:

with open("datafile") as myfile:
    head = [next(myfile) for x in range(N)]
print(head)

Python 2:

with open("datafile") as myfile:
    head = [next(myfile) for x in xrange(N)]
print head

Here's another way (both Python 2 & 3):

from itertools import islice

with open("datafile") as myfile:
    head = list(islice(myfile, N))
print(head)

How to print the first N lines of a file in python with N as argument

Arguments are available via the sys package.

---

Example 1: ./file.py datafile 10

#!/usr/bin/env python3

import sys

myfile = sys.argv[1]
N = int(sys.argv[2])

with open("datafile") as myfile:
    head = myfile.readlines()[0:args.N]
print(head)

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Example 2: ./file.py datafile --N 10

If you want to pass multiple optional arguments you should have a look at the argparse package.

#!/usr/bin/env python3

import argparse

parser = argparse.ArgumentParser(description='Read head of file.')
parser.add_argument('file', help='Textfile to read')
parser.add_argument('--N', type=int, default=10, help='Number of lines to read')

args = parser.parse_args()
with open(args.file) as myfile:
    head = myfile.readlines()[0:args.N]
print(head)

How to read first N lines of a text file and write it to another text file?

Well, you have it right, using islice(filename, n) will get you the first n lines of file filename. The problem here is when you try and write these lines to another file.

The error is pretty intuitive (I've added the full error one receives in this case):

TypeError: write() argument must be str, not list

This is because f.write() accepts strings as parameters, not list types.

So, instead of dumping the list as is, write the contents of it in your other file using a for loop:

with open("input.txt", "r") as myfile:
    head = list(islice(myfile, 3))

# always remember, use files in a with statement
with open("output.txt", "w") as f2:
    for item in head:
        f2.write(item)

Granted that the contents of the list are all of type str this works like a charm; if not, you just need to wrap each item in the for loop in an str() call to make sure it is converted to a string.

If you want an approach that doesn't require a loop, you could always consider using f.writelines() instead of f.write() (and, take a look at Jon's comment for another tip with writelines).

Get first character of each line from string with multiple lines in Python

Try

data = """
Come to the
River
Of my
Soulful
Sentiments
Meandering silently
Yearning for release.
Hasten
Earnestly
As my love flows by
Rushing through the flood-gates
To your heart.
"""

# Get each line into a list by splitting data on every newline
# ['', 'Come to the', 'River', 'Of my', ... 'To your heart.', '']
data_list = data.split("\n")

# Get a list of the first letter of every list element
# use only those elements with length > 0
# ['C', 'R', 'O', 'S', 'S', 'M', 'Y', 'H', 'E', 'A', 'R', 'T']
letters_list = [x[0] for x in data_list if len(x)>0]

# Join it to make one word
# 'CROSSMYHEART'
my_word = ''.join(letters_list)

# Capitalise only the first letter
my_word = my_word.capitalize()

# Print out the answer. 
# 'Crossmyheart'
print(my_word)

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