Related
How do I append to a file instead of overwriting it?
Set the mode in open() to "a" (append) instead of "w" (write):
with open("test.txt", "a") as myfile:
myfile.write("appended text")
The documentation lists all the available modes.
You need to open the file in append mode, by setting "a" or "ab" as the mode. See open().
When you open with "a" mode, the write position will always be at the end of the file (an append). You can open with "a+" to allow reading, seek backwards and read (but all writes will still be at the end of the file!).
Example:
>>> with open('test1','wb') as f:
f.write('test')
>>> with open('test1','ab') as f:
f.write('koko')
>>> with open('test1','rb') as f:
f.read()
'testkoko'
Note: Using 'a' is not the same as opening with 'w' and seeking to the end of the file - consider what might happen if another program opened the file and started writing between the seek and the write. On some operating systems, opening the file with 'a' guarantees that all your following writes will be appended atomically to the end of the file (even as the file grows by other writes).
A few more details about how the "a" mode operates (tested on Linux only). Even if you seek back, every write will append to the end of the file:
>>> f = open('test','a+') # Not using 'with' just to simplify the example REPL session
>>> f.write('hi')
>>> f.seek(0)
>>> f.read()
'hi'
>>> f.seek(0)
>>> f.write('bye') # Will still append despite the seek(0)!
>>> f.seek(0)
>>> f.read()
'hibye'
In fact, the fopen manpage states:
Opening a file in append mode (a as the first character of mode)
causes all subsequent write operations to this stream to occur at
end-of-file, as if preceded the call:
fseek(stream, 0, SEEK_END);
Old simplified answer (not using with):
Example: (in a real program use with to close the file - see the documentation)
>>> open("test","wb").write("test")
>>> open("test","a+b").write("koko")
>>> open("test","rb").read()
'testkoko'
I always do this,
f = open('filename.txt', 'a')
f.write("stuff")
f.close()
It's simple, but very useful.
Python has many variations off of the main three modes, these three modes are:
'w' write text
'r' read text
'a' append text
So to append to a file it's as easy as:
f = open('filename.txt', 'a')
f.write('whatever you want to write here (in append mode) here.')
Then there are the modes that just make your code fewer lines:
'r+' read + write text
'w+' read + write text
'a+' append + read text
Finally, there are the modes of reading/writing in binary format:
'rb' read binary
'wb' write binary
'ab' append binary
'rb+' read + write binary
'wb+' read + write binary
'ab+' append + read binary
You probably want to pass "a" as the mode argument. See the docs for open().
with open("foo", "a") as f:
f.write("cool beans...")
There are other permutations of the mode argument for updating (+), truncating (w) and binary (b) mode but starting with just "a" is your best bet.
You can also do it with print instead of write:
with open('test.txt', 'a') as f:
print('appended text', file=f)
If test.txt doesn't exist, it will be created...
when we using this line open(filename, "a"), that a indicates the appending the file, that means allow to insert extra data to the existing file.
You can just use this following lines to append the text in your file
def FileSave(filename,content):
with open(filename, "a") as myfile:
myfile.write(content)
FileSave("test.txt","test1 \n")
FileSave("test.txt","test2 \n")
The 'a' parameter signifies append mode. If you don't want to use with open each time, you can easily write a function to do it for you:
def append(txt='\nFunction Successfully Executed', file):
with open(file, 'a') as f:
f.write(txt)
If you want to write somewhere else other than the end, you can use 'r+'†:
import os
with open(file, 'r+') as f:
f.seek(0, os.SEEK_END)
f.write("text to add")
Finally, the 'w+' parameter grants even more freedom. Specifically, it allows you to create the file if it doesn't exist, as well as empty the contents of a file that currently exists.
† Credit for this function goes to #Primusa
You can also open the file in r+ mode and then set the file position to the end of the file.
import os
with open('text.txt', 'r+') as f:
f.seek(0, os.SEEK_END)
f.write("text to add")
Opening the file in r+ mode will let you write to other file positions besides the end, while a and a+ force writing to the end.
if you want to append to a file
with open("test.txt", "a") as myfile:
myfile.write("append me")
We declared the variable myfile to open a file named test.txt. Open takes 2 arguments, the file that we want to open and a string that represents the kinds of permission or operation we want to do on the file
here is file mode options
Mode Description
'r' This is the default mode. It Opens file for reading.
'w' This Mode Opens file for writing.
If file does not exist, it creates a new file.
If file exists it truncates the file.
'x' Creates a new file. If file already exists, the operation fails.
'a' Open file in append mode.
If file does not exist, it creates a new file.
't' This is the default mode. It opens in text mode.
'b' This opens in binary mode.
'+' This will open a file for reading and writing (updating)
If multiple processes are writing to the file, you must use append mode or the data will be scrambled. Append mode will make the operating system put every write, at the end of the file irrespective of where the writer thinks his position in the file is. This is a common issue for multi-process services like nginx or apache where multiple instances of the same process, are writing to the same log
file. Consider what happens if you try to seek, then write:
Example does not work well with multiple processes:
f = open("logfile", "w"); f.seek(0, os.SEEK_END); f.write("data to write");
writer1: seek to end of file. position 1000 (for example)
writer2: seek to end of file. position 1000
writer2: write data at position 1000 end of file is now 1000 + length of data.
writer1: write data at position 1000 writer1's data overwrites writer2's data.
By using append mode, the operating system will place any write at the end of the file.
f = open("logfile", "a"); f.seek(0, os.SEEK_END); f.write("data to write");
Append most does not mean, "open file, go to end of the file once after opening it". It means, "open file, every write I do will be at the end of the file".
WARNING: For this to work you must write all your record in one shot, in one write call. If you split the data between multiple writes, other writers can and will get their writes in between yours and mangle your data.
Sometimes, beginners have this problem because they attempt to open and write to a file in a loop:
for item in my_data:
with open('results.txt', 'w') as f:
f.write(some_calculation(item))
The problem is that every time the file is opened for writing, it will be truncated (cleared out).
We can solve this by opening in append mode instead; but in cases like this, it will normally be better to solve the problem by inverting the logic. If the file is opened only once, then it won't get overwritten each time; and we can keep writing to it as long as it is open - we don't have to re-open it for each write (it would be pointless for Python to make things work that way, since it would add to the required code for no benefit).
Thus:
with open('results.txt', 'w') as f:
for item in my_data:
f.write(some_calculation(item))
The simplest way to append more text to the end of a file would be to use:
with open('/path/to/file', 'a+') as file:
file.write("Additions to file")
file.close()
The a+ in the open(...) statement instructs to open the file in append mode and allows read and write access.
It is also always good practice to use file.close() to close any files that you have opened once you are done using them.
python
I have a text file (.txt) and I need to print to the last byte of the txt.
how I do that ?
When I do not know the size of the document.
The documenation provides an API, that can be used to solve that problem. You will need to do the following things in order:
Open the file in text mode like in the example here.
Change the file pointer to the last byte. This can be achieved using the seek memeber function of the file object. Use the SEEK_END token with an offset of -1 to get one byte before the end of the file
Read one byte with the read function.
Print that byte.
If you did not use a context manager (with keyword) while opening the file, you should use close to close the file before exiting the program
The trick here is to use the seek method, that can be used to specify an offset relative to the end of the file.
The following should work:
with open("text.txt") as file:
text = outfile.read()
byte_array = bytearray(text, "utf8")
print(byte_array[-1:])
If you need the binary representation
with open("text.txt") as file:
text = outfile.read()
byte_array = bytearray(text, "utf8")
binary_byte_list = []
for byte in byte_array:
binary_representation = bin(byte)
binary_byte_list.append(binary_representation)
print(binary_byte_list[-1:])
You could do it like this using seek which obviates the need to read the entire file into memory:
import os
with open('foo.txt', 'rb') as foo:
foo.seek(-1, os.SEEK_END)
b = foo.read()
print(b)
In this case the last character is newline and therefore:
Output:
b'\n'
Note:
File opened in binary mode
How do I append to a file instead of overwriting it?
Set the mode in open() to "a" (append) instead of "w" (write):
with open("test.txt", "a") as myfile:
myfile.write("appended text")
The documentation lists all the available modes.
You need to open the file in append mode, by setting "a" or "ab" as the mode. See open().
When you open with "a" mode, the write position will always be at the end of the file (an append). You can open with "a+" to allow reading, seek backwards and read (but all writes will still be at the end of the file!).
Example:
>>> with open('test1','wb') as f:
f.write('test')
>>> with open('test1','ab') as f:
f.write('koko')
>>> with open('test1','rb') as f:
f.read()
'testkoko'
Note: Using 'a' is not the same as opening with 'w' and seeking to the end of the file - consider what might happen if another program opened the file and started writing between the seek and the write. On some operating systems, opening the file with 'a' guarantees that all your following writes will be appended atomically to the end of the file (even as the file grows by other writes).
A few more details about how the "a" mode operates (tested on Linux only). Even if you seek back, every write will append to the end of the file:
>>> f = open('test','a+') # Not using 'with' just to simplify the example REPL session
>>> f.write('hi')
>>> f.seek(0)
>>> f.read()
'hi'
>>> f.seek(0)
>>> f.write('bye') # Will still append despite the seek(0)!
>>> f.seek(0)
>>> f.read()
'hibye'
In fact, the fopen manpage states:
Opening a file in append mode (a as the first character of mode)
causes all subsequent write operations to this stream to occur at
end-of-file, as if preceded the call:
fseek(stream, 0, SEEK_END);
Old simplified answer (not using with):
Example: (in a real program use with to close the file - see the documentation)
>>> open("test","wb").write("test")
>>> open("test","a+b").write("koko")
>>> open("test","rb").read()
'testkoko'
I always do this,
f = open('filename.txt', 'a')
f.write("stuff")
f.close()
It's simple, but very useful.
Python has many variations off of the main three modes, these three modes are:
'w' write text
'r' read text
'a' append text
So to append to a file it's as easy as:
f = open('filename.txt', 'a')
f.write('whatever you want to write here (in append mode) here.')
Then there are the modes that just make your code fewer lines:
'r+' read + write text
'w+' read + write text
'a+' append + read text
Finally, there are the modes of reading/writing in binary format:
'rb' read binary
'wb' write binary
'ab' append binary
'rb+' read + write binary
'wb+' read + write binary
'ab+' append + read binary
You probably want to pass "a" as the mode argument. See the docs for open().
with open("foo", "a") as f:
f.write("cool beans...")
There are other permutations of the mode argument for updating (+), truncating (w) and binary (b) mode but starting with just "a" is your best bet.
You can also do it with print instead of write:
with open('test.txt', 'a') as f:
print('appended text', file=f)
If test.txt doesn't exist, it will be created...
when we using this line open(filename, "a"), that a indicates the appending the file, that means allow to insert extra data to the existing file.
You can just use this following lines to append the text in your file
def FileSave(filename,content):
with open(filename, "a") as myfile:
myfile.write(content)
FileSave("test.txt","test1 \n")
FileSave("test.txt","test2 \n")
The 'a' parameter signifies append mode. If you don't want to use with open each time, you can easily write a function to do it for you:
def append(txt='\nFunction Successfully Executed', file):
with open(file, 'a') as f:
f.write(txt)
If you want to write somewhere else other than the end, you can use 'r+'†:
import os
with open(file, 'r+') as f:
f.seek(0, os.SEEK_END)
f.write("text to add")
Finally, the 'w+' parameter grants even more freedom. Specifically, it allows you to create the file if it doesn't exist, as well as empty the contents of a file that currently exists.
† Credit for this function goes to #Primusa
You can also open the file in r+ mode and then set the file position to the end of the file.
import os
with open('text.txt', 'r+') as f:
f.seek(0, os.SEEK_END)
f.write("text to add")
Opening the file in r+ mode will let you write to other file positions besides the end, while a and a+ force writing to the end.
if you want to append to a file
with open("test.txt", "a") as myfile:
myfile.write("append me")
We declared the variable myfile to open a file named test.txt. Open takes 2 arguments, the file that we want to open and a string that represents the kinds of permission or operation we want to do on the file
here is file mode options
Mode Description
'r' This is the default mode. It Opens file for reading.
'w' This Mode Opens file for writing.
If file does not exist, it creates a new file.
If file exists it truncates the file.
'x' Creates a new file. If file already exists, the operation fails.
'a' Open file in append mode.
If file does not exist, it creates a new file.
't' This is the default mode. It opens in text mode.
'b' This opens in binary mode.
'+' This will open a file for reading and writing (updating)
If multiple processes are writing to the file, you must use append mode or the data will be scrambled. Append mode will make the operating system put every write, at the end of the file irrespective of where the writer thinks his position in the file is. This is a common issue for multi-process services like nginx or apache where multiple instances of the same process, are writing to the same log
file. Consider what happens if you try to seek, then write:
Example does not work well with multiple processes:
f = open("logfile", "w"); f.seek(0, os.SEEK_END); f.write("data to write");
writer1: seek to end of file. position 1000 (for example)
writer2: seek to end of file. position 1000
writer2: write data at position 1000 end of file is now 1000 + length of data.
writer1: write data at position 1000 writer1's data overwrites writer2's data.
By using append mode, the operating system will place any write at the end of the file.
f = open("logfile", "a"); f.seek(0, os.SEEK_END); f.write("data to write");
Append most does not mean, "open file, go to end of the file once after opening it". It means, "open file, every write I do will be at the end of the file".
WARNING: For this to work you must write all your record in one shot, in one write call. If you split the data between multiple writes, other writers can and will get their writes in between yours and mangle your data.
Sometimes, beginners have this problem because they attempt to open and write to a file in a loop:
for item in my_data:
with open('results.txt', 'w') as f:
f.write(some_calculation(item))
The problem is that every time the file is opened for writing, it will be truncated (cleared out).
We can solve this by opening in append mode instead; but in cases like this, it will normally be better to solve the problem by inverting the logic. If the file is opened only once, then it won't get overwritten each time; and we can keep writing to it as long as it is open - we don't have to re-open it for each write (it would be pointless for Python to make things work that way, since it would add to the required code for no benefit).
Thus:
with open('results.txt', 'w') as f:
for item in my_data:
f.write(some_calculation(item))
The simplest way to append more text to the end of a file would be to use:
with open('/path/to/file', 'a+') as file:
file.write("Additions to file")
file.close()
The a+ in the open(...) statement instructs to open the file in append mode and allows read and write access.
It is also always good practice to use file.close() to close any files that you have opened once you are done using them.
I'm trying to make the program that convert all words to uppercase.
a = open("file.txt",encoding='UTF-8')
for b in a:
c = b.rstrip()
print(c.upper())
a.close()
this is my code
it prints uppercase text. But it can't save the file on 'file.txt'.
I want to convert all words to uppercase.
How can I solve it????
Here's how you can do it: [provided that you are working with a small file]
Open the file in read mode store the uppercase text in a variable; then, open another file handler in write mode and write the content into it.
with open('file.txt' , 'r') as input:
y = input.read().upper()
with open('file.txt', 'w') as out:
out.write(y)
You can actually do this "in place" by reading and writing a character at a time.
with open("file.txt", "r") as f:
while (b := f.read(1)) != '':
f.write(b.upper())
This is safe because you are processing the file one byte at a time (and writing one byte for every byte read) and not using seek to potentially overwrite a byte before it is read. The file-like object's underlying buffering and your system's disk cache means this isn't as inefficient as it looks.
(This does make one assumption: that the encoded length of b is always the same as b.upper(). I suspect that should always be true. If not, you should be able to read and write at least a line at a time, though not in place:
with open("input.txt") as inh, open("output.txt", "w") as outh:
for line in inh:
print(line.upper(), file=outh)
)
First convert the txt into the string:
with open('file.txt', 'r') as file:
data = file.read()
And then revise the data to the uppercase:
data_revise = data.upper()
Finally revise the texts in the file:
fout = open('data/try.txt', 'w')
fout.write(data_revise)
You can write all changes to temporary file and replace original after all data processed. You can use either map() or generator expression:
with open(r"C:\original.txt") as inp_f, open(r"C:\temp.txt", "w+") as out_f:
out_f.writelines(map(str.upper, inp_f))
with open(r"C:\original.txt") as inp_f, open(r"C:\temp.txt", "w+") as out_f:
out_f.writelines(s.upper() for s in inp_f)
To replace original file you can use shutil.move():
import shutil
...
shutil.move(r"C:\temp.txt", r"C:\original.txt")
How do I append to a file instead of overwriting it?
Set the mode in open() to "a" (append) instead of "w" (write):
with open("test.txt", "a") as myfile:
myfile.write("appended text")
The documentation lists all the available modes.
You need to open the file in append mode, by setting "a" or "ab" as the mode. See open().
When you open with "a" mode, the write position will always be at the end of the file (an append). You can open with "a+" to allow reading, seek backwards and read (but all writes will still be at the end of the file!).
Example:
>>> with open('test1','wb') as f:
f.write('test')
>>> with open('test1','ab') as f:
f.write('koko')
>>> with open('test1','rb') as f:
f.read()
'testkoko'
Note: Using 'a' is not the same as opening with 'w' and seeking to the end of the file - consider what might happen if another program opened the file and started writing between the seek and the write. On some operating systems, opening the file with 'a' guarantees that all your following writes will be appended atomically to the end of the file (even as the file grows by other writes).
A few more details about how the "a" mode operates (tested on Linux only). Even if you seek back, every write will append to the end of the file:
>>> f = open('test','a+') # Not using 'with' just to simplify the example REPL session
>>> f.write('hi')
>>> f.seek(0)
>>> f.read()
'hi'
>>> f.seek(0)
>>> f.write('bye') # Will still append despite the seek(0)!
>>> f.seek(0)
>>> f.read()
'hibye'
In fact, the fopen manpage states:
Opening a file in append mode (a as the first character of mode)
causes all subsequent write operations to this stream to occur at
end-of-file, as if preceded the call:
fseek(stream, 0, SEEK_END);
Old simplified answer (not using with):
Example: (in a real program use with to close the file - see the documentation)
>>> open("test","wb").write("test")
>>> open("test","a+b").write("koko")
>>> open("test","rb").read()
'testkoko'
I always do this,
f = open('filename.txt', 'a')
f.write("stuff")
f.close()
It's simple, but very useful.
Python has many variations off of the main three modes, these three modes are:
'w' write text
'r' read text
'a' append text
So to append to a file it's as easy as:
f = open('filename.txt', 'a')
f.write('whatever you want to write here (in append mode) here.')
Then there are the modes that just make your code fewer lines:
'r+' read + write text
'w+' read + write text
'a+' append + read text
Finally, there are the modes of reading/writing in binary format:
'rb' read binary
'wb' write binary
'ab' append binary
'rb+' read + write binary
'wb+' read + write binary
'ab+' append + read binary
You probably want to pass "a" as the mode argument. See the docs for open().
with open("foo", "a") as f:
f.write("cool beans...")
There are other permutations of the mode argument for updating (+), truncating (w) and binary (b) mode but starting with just "a" is your best bet.
You can also do it with print instead of write:
with open('test.txt', 'a') as f:
print('appended text', file=f)
If test.txt doesn't exist, it will be created...
when we using this line open(filename, "a"), that a indicates the appending the file, that means allow to insert extra data to the existing file.
You can just use this following lines to append the text in your file
def FileSave(filename,content):
with open(filename, "a") as myfile:
myfile.write(content)
FileSave("test.txt","test1 \n")
FileSave("test.txt","test2 \n")
The 'a' parameter signifies append mode. If you don't want to use with open each time, you can easily write a function to do it for you:
def append(txt='\nFunction Successfully Executed', file):
with open(file, 'a') as f:
f.write(txt)
If you want to write somewhere else other than the end, you can use 'r+'†:
import os
with open(file, 'r+') as f:
f.seek(0, os.SEEK_END)
f.write("text to add")
Finally, the 'w+' parameter grants even more freedom. Specifically, it allows you to create the file if it doesn't exist, as well as empty the contents of a file that currently exists.
† Credit for this function goes to #Primusa
You can also open the file in r+ mode and then set the file position to the end of the file.
import os
with open('text.txt', 'r+') as f:
f.seek(0, os.SEEK_END)
f.write("text to add")
Opening the file in r+ mode will let you write to other file positions besides the end, while a and a+ force writing to the end.
if you want to append to a file
with open("test.txt", "a") as myfile:
myfile.write("append me")
We declared the variable myfile to open a file named test.txt. Open takes 2 arguments, the file that we want to open and a string that represents the kinds of permission or operation we want to do on the file
here is file mode options
Mode Description
'r' This is the default mode. It Opens file for reading.
'w' This Mode Opens file for writing.
If file does not exist, it creates a new file.
If file exists it truncates the file.
'x' Creates a new file. If file already exists, the operation fails.
'a' Open file in append mode.
If file does not exist, it creates a new file.
't' This is the default mode. It opens in text mode.
'b' This opens in binary mode.
'+' This will open a file for reading and writing (updating)
If multiple processes are writing to the file, you must use append mode or the data will be scrambled. Append mode will make the operating system put every write, at the end of the file irrespective of where the writer thinks his position in the file is. This is a common issue for multi-process services like nginx or apache where multiple instances of the same process, are writing to the same log
file. Consider what happens if you try to seek, then write:
Example does not work well with multiple processes:
f = open("logfile", "w"); f.seek(0, os.SEEK_END); f.write("data to write");
writer1: seek to end of file. position 1000 (for example)
writer2: seek to end of file. position 1000
writer2: write data at position 1000 end of file is now 1000 + length of data.
writer1: write data at position 1000 writer1's data overwrites writer2's data.
By using append mode, the operating system will place any write at the end of the file.
f = open("logfile", "a"); f.seek(0, os.SEEK_END); f.write("data to write");
Append most does not mean, "open file, go to end of the file once after opening it". It means, "open file, every write I do will be at the end of the file".
WARNING: For this to work you must write all your record in one shot, in one write call. If you split the data between multiple writes, other writers can and will get their writes in between yours and mangle your data.
Sometimes, beginners have this problem because they attempt to open and write to a file in a loop:
for item in my_data:
with open('results.txt', 'w') as f:
f.write(some_calculation(item))
The problem is that every time the file is opened for writing, it will be truncated (cleared out).
We can solve this by opening in append mode instead; but in cases like this, it will normally be better to solve the problem by inverting the logic. If the file is opened only once, then it won't get overwritten each time; and we can keep writing to it as long as it is open - we don't have to re-open it for each write (it would be pointless for Python to make things work that way, since it would add to the required code for no benefit).
Thus:
with open('results.txt', 'w') as f:
for item in my_data:
f.write(some_calculation(item))
The simplest way to append more text to the end of a file would be to use:
with open('/path/to/file', 'a+') as file:
file.write("Additions to file")
file.close()
The a+ in the open(...) statement instructs to open the file in append mode and allows read and write access.
It is also always good practice to use file.close() to close any files that you have opened once you are done using them.