How to open, read, write and close a file

Open file with default mode

f = open("test.txt") # opening a file from current directory

f = open("c:/temp/readme.txt") #open by specifying full path

Open file with specific mode

f = open("test.txt") # equivalent to 'r' or 'rt'
f = open("test.txt",'w') # write in text mode
f = open("img.bmp",'r+b') # read and write in binary mode
f = open("test.txt",mode = 'r',encoding = 'utf-8')

Mode	Purpose
r	Open for read (default)
w	Open for write. Creates new if not found, Truncates if exists
x	Open exclusively for creation. Fail if file exists
a	Open for append Creates new if not found. Appends if exist
t	Open in text mode (default)
b	Open in binary mode
+	Open for updating - both read and write

Close a file

f = open("test.txt",encoding = 'utf-8')
# perform file operations
f.close()

or better

try:
   f = open("test.txt",encoding = 'utf-8')
   # perform file operations
finally:
   f.close()

Write to a file with open("test.txt",'w',encoding = 'utf-8') as f:
f.write("my first file\n")
f.write("This file\n\n")
f.write("contains three lines\n")

Read a file >>> f = open("test.txt",'r',encoding = 'utf-8')
>>> f.read(4) # read the first 4 data
'This'

>>> f.read(4) # read the next 4 data
' is '

>>> f.read() # read in the rest till end of file
'my first file\nThis file\ncontains three lines\n'

>>> f.read() # further reading returns empty sting
''

Show current file position >>> f.tell() # get the current file position
56

Jump to a file position >>> f.seek(0) # bring file cursor to initial position
0

Read line by line in a for loop

>>> for line in f:
... print(line, end = '')

# the variable line itself would contain newline \n read from the file
# set the end parameter for print() function to avoid double printing newline

Read only one line f.readline() # read one line from the current position

Read all lines from current position to end of file

f.readlines()

Returns a list of lines

e.g.
['first line\n','second line\n','third line\n']

full list of file methods

f = open("test.txt",'r+a',encoding = 'utf-8')

f.method :-

Method	Description
close()	Close an open file. It has no effect if the file is already closed.
detach()	Separate the underlying binary buffer from the `TextIOBase` and return it.
fileno()	Return an integer number (file descriptor) of the file.
flush()	Flush the write buffer of the file stream.
isatty()	Return `True` if the file stream is interactive.
read(`n`)	Read atmost `n` characters form the file. Reads till end of file if it is negative or `None`.
readable()	Returns `True` if the file stream can be read from.
readline(`n`=-1)	Read and return one line from the file. Reads in at most `n` bytes if specified.
readlines(`n`=-1)	Read and return a list of lines from the file. Reads in at most `n` bytes/characters if specified.
seek(`offset`,`from`=`SEEK_SET`)	Change the file position to `offset` bytes, in reference to `from` (start, current, end).
seekable()	Returns `True` if the file stream supports random access.
tell()	Returns the current file location.
truncate(`size`=`None`)	Resize the file stream to `size` bytes. If `size` is not specified, resize to current location.
writable()	Returns `True` if the file stream can be written to.
write(`s`)	Write string `s` to the file and return the number of characters written.
writelines(`lines`)	Write a list of `lines` to the file.