I did example 16 and decided to keep adding to it. I wanted after rewriting the contents to be able to read it right after.
from sys import argv
script, file = argv
print "Do you want to erase the contents of %r?" % file
print "If yes hit RETURN, or CTRL-C to abort."
raw_input()
target = open(file, 'w')
target.truncate()
print "Now you can type new text to the file one line at a time."
line1 = raw_input("line1: ")
line2 = raw_input("line2: ")
line3 = raw_input("line3: ")
print "The data will now be written to the file."
target.write(line1)
target.write('\n')
target.write(line2)
target.write('\n')
target.write(line3)
target.write('\n')
print "Data has been added to the file."
new_data = open(target)
print new_data.read()
After running it when I get to this point I get the syntax error need string to buffer, file found. I know from the beginning the file was opened in 'w' (write mode) so I also tried this:
new_data = open(target, 'r')
print new_data.read()
If you'd like to both read and write a file, use the appropriate mode, such as 'w+', which is similar to 'w' but also allows reading. I would also recommend the with context manager so you don't have to worry about closing the file. You don't need truncate(), either, as explained in this question.
with open(file, 'w+') as target:
# ...your code...
# new_data = open(target) # no need for this
target.seek(0) # this "rewinds" the file
print target.read()
The answer is in the error message, you are trying to pass a file into open() function whereas the first parameter should be a string - a file-name/path-to-file.
This suppose to work:
new_data = open(file, "r")
print new_data
It is more preferred to use the "open resource as" syntax since it automatically flushes and closes resources which you need to do after writing to a file before you can read from it (without seek-ing to the beginning of the file).
print "Do you want to erase the contents of %r?" % file
print "If yes hit RETURN, or CTRL-C to abort."
raw_input()
with open(file, 'w+') as target:
target.truncate()
print "Now you can type new text to the file one line at a time."
line1 = raw_input("line1: ")
line2 = raw_input("line2: ")
line3 = raw_input("line3: ")
print "The data will now be written to the file."
target.write(line1)
target.write('\n')
target.write(line2)
target.write('\n')
target.write(line3)
target.write('\n')
print "Data has been added to the file."
with open(file) as new_data:
print new_data.read()
Related
from sys import argv
script, filename = argv
print ("We're going to erase %r" % filename)
print ("If you don't want to do that, press CTRL-C (^C)")
print ("If you do want that, hit RETURN.")
input("?")
print ("Opening the file...")
target = open(filename, 'r+')
print ("Truncating the file. Goodbye!")
target.truncate()
print ("Enter two lines: ")
line1 = input("Line 1: ")
line2 = input("Line 2: ")
print ("I'm going to write those to the file")
target.write(line1)
target.write('\n')
target.write(line2)
print (target.read())
print ("Closing file")
target.close()
When I run the script, the interpreter acts like there is no print (target.read()) line. If I close target before that line, and make a new variable like:
txt = open(filename, 'r+')
and then print (txt.read()), it works.
Can someome explain why it doesn't work like I did it above?
Think of working with files as having 2 pointers, one is the variable for the file itself, and the second as a pointer to where in the file you are currently at.
You first target.truncate the file to empty the contents, pointer is at the first character in the file.
Then you give 3 target.write commands, to which the pointer will move to the end of each line as that command is finished.
Finally, you attempt a target.read. At this point the cursor is at the end of the file, and there is nothing to read from that point, moving forward. If you want to read the contents of the file, then you will either need to close and reopen the file, or perform a target.seek(0) to move the pointer to the beginning of the file to the 0th byte before you actually perform a target.read.
When you are writing and reading something in a file you change the file pointer. In this case you are reading the last position in file.
You can add this line before read(), that change the pointer for the first position in file.
target.seek(0)
Looks like it works to me.
from sys import argv
script, filename = argv
print ("We're going to erase %r" % filename)
print ("If you don't want to do that, press CTRL-C (^C)")
print ("If you do want that, hit RETURN.")
input("?")
print ("Opening the file...")
with open(filename, 'w') as target:
print ("Enter two lines: ")
line1 = input("Line 1: ")
line2 = input("Line 2: ")
print ("I'm going to write those to the file")
target.write(line1)
target.write('\n')
target.write(line2)
with open(filename, 'r') as target:
print (target.read())
input ("Closing file")
I'm new to Python, and I am currently learning file operations. I am unable to read from a file, that I just wrote into. I'm using w+ mode.
Also please tell me, what I'm doing wrong in the
textbuffer = str("%r\n %r\n %r\n" % input(), input(), input())
which is commented.
Below is the code snippet:
filename = '/home/ranadeep/PycharmProjects/HelloWorld/ex15_sample.txt'
target = open(filename,'w+')
target.truncate()
print("Input the 3 lines: ")
textbuffer = "Just a demo text input"
#textbuffer = str("%r\n %r\n %r\n" % input(), input(), input())
target.write(textbuffer)
# read not working in w+ mode
print(target.read())
target.close()
# read only mode
updated_target = open(filename,'r')
print(updated_target.read())
with open(file_name,"w+") as f:
f.write("I love programming and i love python ")
f.seek(0) #move cursor to the start of the file
data=f.read()
print(data)
When you write to the file, the line you begin reading from only occurs after the line you wrote to. For this to work, you need to reset the "head" back to the beginning of the file.
target.write("blah")
# This is new
target.seek(0)
print target.read()
target.close()
Below is what my code looks like so far:
restart = 'y'
while (True):
sentence = input("What is your sentence?: ")
sentence_split = sentence.split()
sentence2 = [0]
print(sentence)
for count, i in enumerate(sentence_split):
if sentence_split.count(i) < 2:
sentence2.append(max(sentence2) + 1)
else:
sentence2.append(sentence_split.index(i) +1)
sentence2.remove(0)
print(sentence2)
outfile = open("testing.txt", "wt")
outfile.write(sentence)
outfile.close()
print (outfile)
restart = input("would you like restart the programme y/n?").lower()
if (restart == "n"):
print ("programme terminated")
break
elif (restart == "y"):
pass
else:
print ("Please enter y or n")
I need to know what to do so that my programme opens a file, saves the sentence entered and the numbers that recreate the sentence and then be able print the file. (im guessing this is the read part). As you can probably tell, i know nothing about reading and writing to files, so please write your answer so a noob can understand. Also the one part of the code that is related to files is a complete stab in the dark and taken from different websites so don't think that i have knowledge on this.
Basically, you create a file object by opening it and then do read or write operation
To read a line from a file
#open("filename","mode")
outfile = open("testing.txt", "r")
outfile.readline(sentence)
To read all lines from file
for line in fileobject:
print(line, end='')
To write a file using python
outfile = open("testing.txt", "w")
outfile.write(sentence)
to put it simple, to read a file in python, you need to "open" the file in read mode:
f = open("testing.txt", "r")
The second argument "r" signifies that we open the file to read. After having the file object "f" the content of the file can be accessed by:
content = f.read()
To write a file in python, you need to "open" the file in write mode ("w") or append mode ("a"). If you choose write mode, the old content in the file is lost. If you choose append mode, the new content will be written at the end of the file:
f = open("testing.txt", "w")
To write a string s to that file, we use the write command:
f.write(s)
In your case, it would probably something like:
outfile = open("testing.txt", "a")
outfile.write(sentence)
outfile.close()
readfile = open("testing.txt", "r")
print (readfile.read())
readfile.close()
I would recommend follow the official documentation as pointed out by cricket_007 : https://docs.python.org/3/tutorial/inputoutput.html#reading-and-writing-files
I have the following code:
print "We're going to write to a file you'll be prompted for"
targetfile = raw_input('Enter a filename: ')
targetfilefound = open('targetfile' , 'w')
print "What do we write in this file?"
targetfilefound.write("hello this is working!")
targetfilefound.close()
The script I'm creating should be able to write to a file that the user defines via raw_input. The above could be faulty at core, open to suggestions.
Judging by the stuff the script is printing you probably want the user to input what should be printed to the file so:
print "We're going to write to a file you'll be prompted for"
targetfile = raw_input('Enter a filename: ')
targetfilefound = open(targetfile , 'w')
print "What do we write in this file?"
targetfilefound.write(raw_input())
targetfilefound.close()
Note: This method will create the new file if it does not exist. If you want to check whether the file exists you can use the os module, something like this:
import os
print "We're going to write to a file you'll be prompted for"
targetfile = raw_input('Enter a filename: ')
if os.path.isfile(targetfile) == True:
targetfilefound = open(targetfile , 'w')
print "What do we write in this file?"
targetfilefound.write(raw_input())
targetfilefound.close()
else:
print "File does not exist, do you want to create it? (Y/n)"
action = raw_input('> ')
if action == 'Y' or action == 'y':
targetfilefound = open(targetfile , 'w')
print "What do we write in this file?"
targetfilefound.write(raw_input())
targetfilefound.close()
else:
print "No action taken"
As pointed out by others, remove the quotes from target file as you have assigned it already to a variable.
But actually instead of writing as code you can use the with open as given below
with open('somefile.txt', 'a') as the_file:
the_file.write('hello this is working!\n')
In the above case, you don't need to do any exception handling while processing the file. When-ever an error occurs the file cursor object is automatically closed and we dont need to explicitly close it. Even it writing to file it success, it will automatically close the file pointer reference.
Explanation of efficient use of with from Pershing Programming blog
I am a newbie to Python and was reading up about files from the Python Tutorial
So , I made a small program to practice file handling :
from sys import *
script , file_name = argv
print "Your file is : %s" %file_name
print "Opening the file..."
temp = open(file_name, 'r+')
print "Truncating the file "
temp.truncate()
print "Enter three lines."
line1 = raw_input("line 1: ")
line2 = raw_input("line 2: ")
line3 = raw_input("line 3: ")
print "Writing these to the file."
temp.write(line1)
temp.write("\n")
temp.write(line2)
temp.write("\n")
temp.write(line3)
temp.write("\n")
#for line in temp:
#print line
#temp.read()
print "Closing it."
temp.close()
My Question:
Somehow I am not able to print the content of the file to the terminal using either of the commented (#) statements in the code above . Can someone help me out ?
When you're appending to the file, python is reading from where your "cursor" is in the file, which is at the end.
You need to close the file and open it as "r", and then you will be able to index the contents from the beginning.
You can add a line
temp.seek(0,0)
before
for line in temp:
print line
temp.read()
Thus set the pointer to the beginning of the file again.
For more information about seek(), see https://stackoverflow.com/a/11696554/1686094