I have observed this unusual behaviour when I try to do a string slicing on the words in a file and the words in a list.Both the results are quite different.
For example I have a file 'words.txt' which contains the following content
POPE
POPS
ROPE
POKE
COPE
PAPE
NOPE
POLE
When I write the below piece of code, I expect to get a list of words with last letter omitted.
with open("words.txt", "r") as fo:
for l in fo:
print(l[:-1])
But instead I get this result below.No string slicing takes place and the words are similar as before.
POPE
POPS
ROPE
POKE
COPE
PAPE
NOPE
POLE
But if I write the below code, I get what I want
lis = ["POPE", "POPS", "ROPE", "POKE", "COPE", "PAPE", "NOPE", "POLE"]
for i in lis:
print(i[:-1])
I am able to delete the last letter of each of the words as expected.
POP
POP
ROP
POK
COP
PAP
NOP
POL
So why do I see two different results for the same operation [: -1] ?
The line ends with \n in files where as you dont need line endings in lists.
Your actual file contents are as follows
POPE\n
POPS\n
ROPE\n
POKE\n
COPE\n
PAPE\n
NOPE\n
POLE\n
hence the print(l[:-1]) is actually trimming the line ending i.e. \n.
To verify this, declare an empty list before the loop, and add each line to that list and print it. You will find the that the lines contain the \n on every line
stuff = []
with open("words.txt", "r") as fo:
for line in fo:
stuff.append(line)
print stuff
this will print ['POPE\n', 'POPS\n', 'ROPE\n', 'POKE\n']
If I am not wrong, you want to carry out the slicing operation on the file contents. I think you should look into strip() method.
Related
Open the file romeo.txt and read it line by line. For each line, split the line into a list of words using the split() method. The program should build a list of words. For each word on each line check to see if the word is already in the list and if not append it to the list. When the program completes, sort and print the resulting words in alphabetical order.
This is the question my problem is I cannot write a proper code and gathering true data, always my code gives me 4 different lists for each raw!
** This is my code**
fname = input("Enter file name: ")
fh = open(fname)
lst = list()
for line in fh:
line=line.rstrip()
line =line.split()
if line in last:
print(true)
else:
lst.append(line)
print(lst)
*** the text is here, please copy and paste in text editor***
But soft what light through yonder window breaks
It is the east and Juliet is the sun
Arise fair sun and kill the envious moon
Who is already sick and pale with grief
You are not checking the presence of individual words in the list, but rather the presence of the entire list of words in that line.
With some modifications, you can achieve what you are trying to do this way:
fname = input("Enter file name: ")
fh = open(fname)
lst = list()
for line in fh:
line = line.rstrip()
words = line.split()
for word in words:
if word not in lst:
lst.append(word)
print(lst)
However, a few things I would like to point out looking at your code:
Why are you using rstrip() instead of strip()?
It is better to use list = [] as opposed to your lst = list(). It is shorter, faster, more Pythonic and avoids the use of this confusing lst variable.
You should want to remove punctuation marks attached to words, eg: ,.: which do not get removed by split()
If you want a loop body to not do anything, use pass. Why are you printing true? Also, in Python, it's True and not true.
I am a beginner in python, working on a small logic, i have a text file with html links in it, line by line. I have to read each line of the file, and print the individual links with same prefix and suffix,
so that the model looks like this.
<item>LINK1</item>
<item>LINK2</item>
<item>LINK3</item>
and so on.
I have tried this code, but something is wrong in my approach,
def file_read(fname):
with open(fname) as f:
#Content_list is the list that contains the read lines.
content_list = f.readlines()
for i in content_list:
print(str("<item>") + i + str("</item>"))
file_read(r"C:\Users\mandy\Desktop\gd.txt")
In the output, the suffix was not as expected, as i am a beginner, can anyone sort this out for me?
<item>www.google.com
</item>
<item>www.bing.com
</item>
I think when you use .readLine you also put the end of line character into i.
If i understand you correctly and you want to print
item www.google.com item
Then try
https://www.journaldev.com/23625/python-trim-string-rstrip-lstrip-strip
print(str("") + i.strip() + str(""))
When you use the readlines() method, it also includes the newline character from your file ("\n") before parsing the next line.
You could use a method called .strip() which strips off spaces or newline characters from the beginning and end of each line which would correctly format your code.
def file_read(fname):
with open(fname) as f:
#Content_list is the list that contains the read lines.
content_list = f.readlines()
for i in content_list:
print(str("<item>") + i.strip() + str("</item>"))
file_read(r"C:\Users\mandy\Desktop\gd.txt")
I assume you wanted to print in the following way
www.google.com
When you use readlines it gives extra '\n' at end of each line. to avoid that you can strip the string and in printing you can use fstrings.
with open(fname) as f:
lin=f.readlines()
for i in lin:
print(f"<item>{i.strip()}<item>")
Another method:
with open('stacksource') as f:
lin=f.read().splitlines()
for i in lin:
print(f"<item>{i}<item>")
Here splitlines() splits the lines and gives a list
# open file in read mode
f=open(text_file,'r')
# iterate over the file object
for line in f.read():
print(line)
# close the file
f.close()
the content of file is "Congratulations you have successfully opened the file"! when i try to run this code the output comes in following form:
c (newline) o (newline) n (newline) g.................
...... that is each character is printed individually on a new line because i used read()! but with readline it gives the answer in a single line! why is it so?
r.read() returns one string will all characters (the full file content).
Iterating a string iterates it character wise.
Use
for line in f: # no read()
instead to iterate line wise.
f.read() returns the whole file in a string. for i in iterates something. For a string, it iterates over its characters.
For readline(), it should not print the line. It would read the first line of the file, then print it character by character, like read. Is it possible that you used readlines(), which returns the lines as a list.
One more thing: there is with which takes a "closable" object and auto-closes it at the end of scope. And you can iterate over a file object. So, your code can be improved like this:
with open(text_file, 'r') as f:
for i in f:
print(i)
So i'm writting an anonymizer and I'm having trouble with figuring out, how to replace a Name in a textfile. I have an array with names that should get anonymized, refered here as text here's my code, it should go into an other file and check if the words match, and if true, it should get replaced. As programming is still a foreign language to me, I would love to read a comprehensive answer
for words in fin_message:
if words == text :
new_list = words.replace(text, "xxx")
print(new_list)
else:
print(words)
Since text is a list, you can't directly compare it to "word", but you can test whether the word is in text:
...
if words in text:
print("xxx")
...
This will, however, print the words in the text file one by one. If instead, you want to print the text file as-is, except for the replacements, you could iterate over the lines of the file, and inside the lines over the banned names. Something like this:
banned_words = ["Peter", "Paul", "Mary"]
with open("my_file.txt") as f:
for line in f:
for forbidden in banned_words:
line.replace(forbidden, "xxx")
print(line)
New to programming, looking for a deeper understanding on whats happening.
Goal: open a file and print the first 10 lines. (similar to head command)
Code:
with open('file') as f:
for i in range(0,10):
print([line.strip('\n') for line in f][i])
Result: prints first line fine, then returns the out of range error
File: Is a simple text file with 20 lines, no more than 50 chars per line
FYI - Removed range line and printed both type(list) and length(20). Printed specific indexes without issue (unless >1 in a row)
Able to get the desired result with different code, but trying to improve using with/as
You can actually iterate over a file. Which is what you should be doing here.
with open('file') as f:
for i, line in enumerate(file, start=1):
# Get out of the loop if we hit 10 lines
if i >= 10:
break
# Line already has a '\n' at the end
print(line, end='')
The reason that your code is failing is because of your list comprehension:
[line.strip('\n') for line in f]
The first time through your loop that consumes all of the lines in your file. Now your file has no more lines, so the next time through it creates a list of all the lines in your file and tries to get the [1]st element. But that doesn't exist because there are no lines at the end of your file.
If you wanted to keep your code mostly as-is you could do
lines = [line.rstrip('\n') for line in f]
for i in range(10):
print(lines[i])
But that's also silly, because you could just do
lines = f.readlines()
But that's also silly if you just want up to the 10th line, because you could do this:
with open('file') as f:
print('\n'.join(f.readlines()[:10]))
Some further explanation:
The shortest and worst way you could fix your code is by adding one line of code:
with open('file') as f:
for i in range(0,10):
f.seek(0) # Add this line
print([line.strip('\n') for line in f][i])
Now your code will work - but this is a horrible way to get your code to work. The reason that your code isn't working the way you expect in the first place is that files are consumable iterators. That means that when you read from them eventually you run out of things to read. Here's a simple example:
import io
file = io.StringIO('''
This is is a file
It has some lines
okay, only three.
'''.strip())
for line in file:
print(file.tell(), repr(line))
This outputs
18 'This is is a file\n'
36 'It has some lines\n'
53 'okay, only three.'
Now if you try to read from the file:
print(file.read())
You'll see that it doesn't output anything. That's because you've "consumed" the file. I mean obviously it's still on disk, but the iterator has reached the end of the file. But as shown, you can seek in the file.
print(file.tell())
file.seek(0)
print(file.tell())
print(file.read())
And you'll see your entire file printed. But what about those other positions?
file.seek(36)
print(file.read()) # => okay, only three.
As a side note, you can also specify how much to read:
file.seek(36)
print(file.read(4)) # => okay
print(file.tell()) # => 40
So when we read from a file or iterate over it we consume the iterator and get to the end of the file. Let's put your new tools to work and go back to your original code and explore what's happening.
with open('file') as f:
print(f.tell())
lines = [line.rstrip('\n') for line in f]
print(f.tell())
print(len([line for line in f]))
print(lines)
You'll see that you're at a different location in the file. And the second list comprehension produces an empty list. That's because when a list comprehension is evaluated it executes immediately. So when you do this:
for i in range(10):
print([line.strip('\n') for line in f][i])
What you're doing the first time, i = 0 and then the list comprehension reads to the end of the file. Now it takes the [0]th element of the list, or the first line in the file. But your file iterator is at the end of the file.
So now we get back to the beginning of the list and i = 1. Now we iterate to the end of the file, but we're already at the end so there are no lines to read, and we've got an empty list [] that we try to get the [0]th element of. But there's nothing there. So we get an IndexError.
List comprehensions can be useful, but when you're beginning it's usually much easier to write a for loop and then turn it into a list comprehension. So you might write something like this:
with open('file') as f:
for i, line in enumerate(file, start=10):
if i < 10:
print(line.rstrip())
Now, we shouldn't print inside a list comprehension, so instead we'll collect everything. We start out by putting what we want:
[line.rstrip()
Now add the for bit:
[line.rstrip() for i, line in enumerate(f)
And finally add the filter and our closing brace:
[line.rstrip() for i, line in enumerate(f) if i < 10]
For more on list comprehensions, this is a fantastic resource: http://treyhunner.com/2015/12/python-list-comprehensions-now-in-color/