Python: how to avoid append an empty string in a for loop?

Question

The goal of my codes are to write a function and return a list of strings, in which the successive strings (fruit name) correspond to the consecutive #No.1...#No.5 . The whole name of the fruit was split over multiple lines, and I want to display the fruit name in the list as a single string with no whitespace. I expect my codes return:

['Pear', 'Apple', 'Cherry', 'Banana', 'Peach']

but I got:

['', 'Pear', 'Apple', 'Cherry', 'Banana', 'Peach']

These are the contents of my file fruit.txt:

#NO.1
P
ear
#NO.2
A
pp
l
e
#NO.3
Cherry
#NO.4
Banan
a
#NO.5
Pea
c
h

These are my codes:

def read(filename): 

    myfile = open('fruit', 'r')
    seq = ''
    list1 = []
    for line in myfile:

        if line[0] != '#':
            seq +=line.rstrip('\n')
        else:

            list1.append(seq)
            seq = ''

    list1.append(seq)    
    return list1

how to avoid to append an empty string which is not what I want? I suppose I just need to adjust the position a certain line of codes, any suggestion is appreciated.

Please note that your function will result in a memory leak if called repeatedly. You should never open a file without making sure it is subsequently closed. The easiest way to do this is by using the with construct. For further reading, see this link: effbot.org/zone/python-with-statement.htm — sobek
– sobek, Commented Jan 2, 2017 at 16:28

NPE · Accepted Answer · 2017-01-02 16:20:13Z

4

You could change the

    else:

to

    elif seq:

This checks whether seq is empty and only appends it if it's not.

answered Jan 2, 2017 at 16:20

NPE

503k114 gold badges970 silver badges1k bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Oxymoron88 · Accepted Answer · 2017-01-02 16:36:14Z

1

Alternative if you'd like a single line solution:

with open('fruit.txt') as f:
    content = f.read()

output = [''.join(x.split('\n')[1:len(x.split('\n'))+1]) for x in content.split('#') if len(x.split('\n')) > 1]

answered Jan 2, 2017 at 16:36

Oxymoron88

4953 silver badges9 bronze badges

1 Comment

Jassy.W Over a year ago

Good solution, Thank you!

Hugo G · Accepted Answer · 2017-01-02 16:41:12Z

1

Quick fix for removing empty strings from a list:

list1 = filter(None, list1)

How about this solution with regex? The following is a two-step process. First all whitespace like newlines, spaces etc. is removed. Then all words following your pattern #No.\d are found:

import re

whitespace = re.compile(r'\s*')
fruitdef = re.compile(r'#NO\.\d(\w*)')
inputfile = open('fruit', 'r').read()

inputstring = re.sub(whitespace, '', inputfile)
fruits = re.findall(fruitdef, inputstring)

print fruits

['Pear', 'Apple', 'Cherry', 'Banana', 'Peach']

Minified to a oneliner:

import re

print re.findall(r'#NO\.\d(\w*)', re.sub(r'\s*', '', open('fruit', 'r').read()))

edited Jan 2, 2017 at 16:41

answered Jan 2, 2017 at 16:34

Hugo G

16.7k9 gold badges62 silver badges82 bronze badges

Collectives™ on Stack Overflow

Python: how to avoid append an empty string in a for loop?

3 Answers 3

Comments

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related