I am able to write to a text file using .write(). But after I close() the file and open it again all the written data is gone...? Is there any way that I can permanently save this data on the file?
def writeToFile():
myFile = open("myText.txt","w")
for each in range(8,10):
record = "This is record number {} in the file\n".format(each)
myFile.write(record)
myFile.close()
writeToFile()
So what i meant was that the first time i run this program it appends to the file. After this when i close the program and run it again i want it to write to the file again, but instead it only overrides it, i.e the earlier data is deleted each time i close the program.
The data you wanted to write was indeed permanently written... until you opened again overwriting the previous data.
You have different modes to open the file.
If you know that the file has important data and only want to read it, use this mode.
file = open('./path_to_file', 'r')
If you want to overwrite the data, use this one instead:
file = open('./path_to_file', 'w')
Optionally, you can use this other way instead, and it will close the file for you.
with open('./path_to_file', 'r') as read_file:
for line in read_file:
print line
This will open the file, read it line by line writing it on the screen and closing it for you at the end.
Finally, if you need to open it again and append new content at the end of the file, just use this:
file = open('./path_to_file', 'a')
Related
I want to save ''contents'' to a new text file in python. I need to have all the words in lowercase to be able to find the word frequency. '''text.lower()''' didn't work. Here is the code;
text=open('page.txt', encoding='utf8')
for x in text:
print(x.lower())
I want to save the results of print to a new text file. How can I do that?
You can use file parameter in print to directly print the output of print(...) to your desired file.
text=open('page.txt', encoding='utf8')
text1=open('page1.txt', mode='x',encoding='utf8') #New text file name it according to you
for x in text:
print(x.lower(),file=text1)
text.close()
text1.close()
Note: Use with while operating on files. As you don't have to explicitly use .close it takes care of that.
You are opening the file page.txt for reading, but it's not open to write. Since you want to save to a new text file, you might also open new_page.txt where you write all of the lines in page.txt lowercased:
# the with statement is the more pythonic way to open a file
with open('page.txt') as fh:
# open the new file handle in write mode ('w' is for write,
# it defaults to 'r' for read
with open('new_page.txt', 'w') as outfile:
for line in fh:
# write the lowercased version of each line to the new file
outfile.write(line.lower())
The important thing to note is that the with statement negates the need for you to close the file, even in the case of an error
import sys
stdoutOrigin=sys.stdout
sys.stdout = open("yourfilename.txt", "w")
#Do whatever you need to write on the file here.
sys.stdout.close()
sys.stdout=stdoutOrigin
So I would like to know how to save and check different values in a file. I have tried to read a file
with open(filename, 'r') as f:
varName = f.readline()
and this to write things to a file however this overwrites anything already in the file
with open('topname.txt', 'w') as f:
f.write(str(name))
f.close()
another problem is when I want to check the values by using a for loop however that didn't work. I was wondering if there was any other way to check, read and write values to/from a file.
An example of this is a login page where people can make accounts and log in and the program checks if the username and password exist.
When I looked on the internet it talked about a thing called pickle but it wasn't the same thing as what I wanted from what I could see.
For your first question, you need to open the file in append mode:
with open('topname.txt', 'a+') as f:
f.write(str(name))
f.close()
The '+' sign in append mode indicates that the script will create a new file if it doesn't already exist, if it does, it'll just append to it.
You want to "append" to the file, so open it with mode 'a' instead of 'w'.
Also, do not call f.close() inside of the with block. with will close the file for you after the block.
with open('topname.txt', 'a') as f:
f.write(str(name))
See: https://docs.python.org/3.6/library/functions.html#open
To append data to an existing file use open("Filename", "a") for "append mode." This is in contrast to your "read" and "write" modes.
if you want to read ,write and update, you need to open file file = open('topname.txt', 'a+') and to check every line to match user data for line in file:print(line) .Other operations like file.read(), file.write() will help. Remember to release resources by closing file finally file.close()
If I want to open a file, unpickle an object inside it, then overwrite it later, is it okay to just use
data = {} #Its a dictionary in my code
file = open("filename","wb")
data = pickle.load(file)
data["foo"] = "bar"
pickle.dump(data,file)
file.close()
Or would I have to use "rb" first and then use "wb" later (using with statements for each) which is what I am doing now. Note that in my program, there is a hashing algorithm in between opening the file and closing it, which is where the dictionary data comes from, and I basically want to be able to only open the file once without having to do two with statements
If you want to read, then write the file, do not use modes involving w at all; all of them truncate the file on opening it.
If the file is known to exist, use mode "rb+", which opens an existing file for both read and write.
Your code only needs to change a tiny bit:
# Open using with statement to ensure prompt/proper closing
with open("filename","rb+") as file:
data = pickle.load(file) # Load from file (moves file pointer to end of file)
data["foo"] = "bar"
file.seek(0) # Move file pointer back to beginning of file
pickle.dump(data, file) # Write new data over beginning of file
file.truncate() # If new dump is smaller, make sure to chop off excess data
You can use wb+ which opens the file for both reading and writing
This question is helpful for understanding the differences between each of pythons read and write conditions, but adding + at the end usually always opens the file for both read and write
Confused by python file mode "w+"
I'm trying to pull some data from Facebook pages for a product and dump it all into a text file, but I find that the file keeps overwriting itself with the data. I'm not sure if it's a pagination issue or if I have to make several files.
Here's my code:
#Modules
import requests
import facebook
import json
def some_action(post):
print posts['data']
print post['created_time']
#Token
access_token = 'INSERT ACCESS TOKEN'
user = 'walkers'
#Posts
graph = facebook.GraphAPI(access_token)
profile = graph.get_object(user)
posts = graph.get_connections(profile['id'], 'posts')
#Write
while True:
posts = requests.get(posts['paging']['next']).json()
#print posts
with open('test121.txt', 'w') as outfile:
json.dump(posts, outfile)
Any idea as to why this is happening?
w overwrites, open with a to append or open the file once outside the loop:
append:
while True:
posts = requests.get(posts['paging']['next']).json()
#print posts
with open('test121.txt', 'a') as outfile:
json.dump(posts, outfile)
Open once outside the loop:
with open('test121.txt', 'w') as outfile:
while True:
posts = requests.get(posts['paging']['next']).json()
#print posts
json.dump(posts, outfile)
It makes more sense to use the second option, if you are going to be running the code multiple times then you can open with a outside the loop also, if the file does not exist it will be created, if it does data will be appended
This is because you are using the file operator with w mode, you are overwriting the content. You can use the a append mode:
It can be done like this
Modification:
with open('test121.txt', 'w') as outfile:
while True:
posts = requests.get(posts['paging']['next']).json()
json.dump(posts, outfile)
w overwrites on the existing file
i.e)
File1.txt:
123
code:
with open("File1.txt","w") as oup1:
oup1.write("2")
File1.txt after python run:
2
Its value is overwritten
a appends to the existing file
i.e)
File1.txt:
123
code:
with open("File1.txt","a") as oup1:
oup1.write("2")
File1.txt after python run:
1232
The written content is appended to the end.
Opening and Closing Files
to use actual data files reading and writing to the standard input and output.
Python provides basic functions and methods necessary to manipulate files by default. You can do your most of the file manipulation using a file object.
The open Function
Before you can read or write a file, you have to open it using Python's built-in open() function. This function creates a file object, which would be utilized to call other support methods associated with it.
Syntax
file object = open(file_name [, access_mode][, buffering])
Here are parameter details:
file_name: The file_name argument is a string value that contains the name of the file that you want to access.
access_mode: The access_mode determines the mode in which the file has to be opened, i.e., read, write, append, etc. A complete list of possible values is given below in the table. This is optional parameter and the default file access mode is read (r).
buffering: If the buffering value is set to 0, no buffering takes place. If the buffering value is 1, line buffering is performed while accessing a file. If you specify the buffering value as an integer greater than 1, then buffering action is performed with the indicated buffer size. If negative, the buffer size is the system default(default behavior).
Here is a list of the different modes of opening a file −
Modes and Description
r= Opens a file for reading only. The file pointer is placed at the beginning of the file. This is the default mode.
rb= Opens a file for reading only in binary format. The file pointer is placed at the beginning of the file. This is the default mode.
r+= Opens a file for both reading and writing. The file pointer placed at the beginning of the file.
rb+= Opens a file for both reading and writing in binary format. The file pointer placed at the beginning of the file.
w= Opens a file for writing only. Overwrites the file if the file exists. If the file does not exist, creates a new file for writing.
wb= Opens a file for writing only in binary format. Overwrites the file if the file exists. If the file does not exist, creates a new file for writing.
w+= Opens a file for both writing and reading. Overwrites the existing file if the file exists. If the file does not exist, creates a new file for reading and writing.
wb+= Opens a file for both writing and reading in binary format. Overwrites the existing file if the file exists. If the file does not exist, creates a new file for reading and writing.
a= Opens a file for appending. The file pointer is at the end of the file if the file exists. That is, the file is in the append mode. If the file does not exist, it creates a new file for writing.
ab= Opens a file for appending in binary format. The file pointer is at the end of the file if the file exists. That is, the file is in the append mode. If the file does not exist, it creates a new file for writing.
a+= Opens a file for both appending and reading. The file pointer is at the end of the file if the file exists. The file opens in the append mode. If the file does not exist, it creates a new file for reading and writing.
ab+= Opens a file for both appending and reading in binary format. The file pointer is at the end of the file if the file exists. The file opens in the append mode. If the file does not exist, it creates a new file for reading and writing.
Reading and Writing Files
The file object provides a set of access methods to make our lives easie with the use of read() and write() methods to read and write files.
The write() Method
The write() method writes any string to an open file. It is important to note that Python strings can have binary data and not just text.
The write() method does not add a newline character ('\n') to the end of the string −
Syntax
fileObject.write(string);
Here, passed parameter is the content to be written into the opened file.
Example
# Open a file
fo = open("file.txt", "wb")
fo.write( "Python is a great language");
# Closeopend file
fo.close()
The above method would create foo.txt file and would write given content in that file and finally it would close that file. If you would open this file, it would have following content.
Python is a great language.
The read() Method
The read() method reads a string from an open file. It is important to note that Python strings can have binary data. apart from text data.
Syntax
fileObject.read([count]);
Here, passed parameter is the number of bytes to be read from the opened file. This method starts reading from the beginning of the file and if count is missing, then it tries to read as much as possible, maybe until the end of file.
Example
Let's take a file foo.txt, which we created above.
# Open a file
fo = open("foo.txt", "r+")
str = fo.read(10);
print "Read String is : ", str
# Close opend file
fo.close()
This produces the following result −
Read String is : Python is
Hey I need to split a large file in python into smaller files that contain only specific lines. How do I do this?
You're probably going to want to do something like this:
big_file = open('big_file', 'r')
small_file1 = open('small_file1', 'w')
small_file2 = open('small_file2', 'w')
for line in big_file:
if 'Charlie' in line: small_file1.write(line)
if 'Mark' in line: small_file2.write(line)
big_file.close()
small_file1.close()
small_file2.close()
Opening a file for reading returns an object that allows you to iterate over the lines. You can then check each line (which is just a string of whatever that line contains) for whatever condition you want, then write it to the appropriate file that you opened for writing. It is worth noting that when you open a file with 'w' it will overwrite anything already written to that file. If you want to simply add to the end, you should open it with 'a', to append.
Additionally, if you expect there to be some possibility of error in your reading/writing code, and want to make sure the files are closed, you can use:
with open('big_file', 'r') as big_file:
<do stuff prone to error>
Do you mean breaking it down into subsections? Like if I had a file with chapter 1, chapter 2, and chapter 3, you want it to be broken down into separate files for each chapter?
The way I've done this is similar to Wilduck's response, but closes the input file as soon as it reads in the data and keeps all the lines read in.
data_file = open('large_file_name', 'r')
lines = data_file.readlines()
data_file.close()
outputFile = open('output_file_one', 'w')
for line in lines:
if 'SomeName' in line:
outputFile.write(line)
outputFile.close()
If you wanted to have more than one output file you could either add more loops or open more than one outputFile at a time.
I'd recommend using Wilducks response, however, as it uses less space and will take less time with larger files since the file is read only once.
How big and does it need to be done in python? If this is on unix, would split/csplit/grep suffice?
First, open the big file for reading.
Second, open all the smaller file names for writing.
Third, iterate through every line. Every iteration, check to see what kind of line it is, then write it to that file.
More info on File I/O: http://docs.python.org/tutorial/inputoutput.html