File Operations

Opening a File

Besides computation, a computer must be able to store data, usually in files. Python directly provides file I/O (Input/Output) functions that make reading and writing convenient.

The open() function opens a file. If no mode is specified, it defaults to r (read-only mode).

open(file, mode='r', buffering=-1, encoding=None,
	 errors=None, newline=None, closefd=True, opener=None)

Mode	Description
`r`	Open read-only; this is the default
`w`	Open for writing; overwrite an existing file or create a missing file
`x`	Create a new file for writing; fail if it already exists
`a`	Append content
`b`	Binary mode
`t`	Text mode (default)
`+`	Open for updating (reading and writing)

Opening a nonexistent path in read-only mode raises FileNotFoundError.

File operations

file = open(file="data.txt", mode="w")
print("File name: %s" % file.name)
print("Mode: %s" % file.mode)
print("Status: %s" % file.closed)
print("Closing...")
file.close()
print("Status: %s" % file.closed)

Output

File name: data.txt
Mode: w
Status: False
Closing...
Status: True

Reading and Writing Files

After opening a file with open(), use the resulting file object to read and write.

A file opened for reading can be read line by line in a loop. Python also simplifies this: the file object itself is iterable, and each iteration reads one line separated by newline characters.

Method	Description
`close()`	Close the file resource
`fileno()`	Get the file descriptor
`flush()`	Force the buffer to flush
`read(n=-1)`	Read data; by default, read everything
`readlines(hint=-1)`	Read all data lines
`readline(size=-1)`	Read one line
`truncate(size=None)`	Truncate the file
`writable()`	Check whether writing is allowed
`write(s)`	Write to the file
`writelines(lines)`	Write a sequence of strings

Since developers must ultimately close every file object, a with statement can close resources automatically. Managing resource acquisition and release with with is an important Python technique that greatly simplifies code structure.

Reading a file

with open(file="data.txt", mode="r", encoding="utf-8") as file:
	for line in file:
		print(line, end='')

data.txt

Alice 16
Bob 17
Terry 21

Output

Alice 16
Bob 17
Terry 21

Writing a file

with open(file="data.txt", mode="w", encoding="utf-8") as file:
	info = {"Alice": 16, "Bob": 17, "Terry": 21}
	for name, age in info.items():
		file.write("%s %d\n" % (name, age))

Output: data.txt

Alice 16
Bob 17
Terry 21

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QUESTION

data.txt already exists. Which mode erases its old content on opening?

QUESTION

After leaving with open(...) as file, what is file.closed?

scores.txt contains the three records below. Write a Python program that reads each line, writes records with a score of at least 18 to selected.txt, replacing any old output, then reopens it in append mode to add Selected: 2. Use UTF-8 and with; keep the input unchanged.

TEXT

Maya 19
Noah 16
Iris 22

File Operations

Opening a File

Besides computation, a computer must be able to store data, usually in files. Python directly provides file I/O (Input/Output) functions that make reading and writing convenient.

The open() function opens a file. If no mode is specified, it defaults to r (read-only mode).

open(file, mode='r', buffering=-1, encoding=None,
	 errors=None, newline=None, closefd=True, opener=None)

Mode	Description
`r`	Open read-only; this is the default
`w`	Open for writing; overwrite an existing file or create a missing file
`x`	Create a new file for writing; fail if it already exists
`a`	Append content
`b`	Binary mode
`t`	Text mode (default)
`+`	Open for updating (reading and writing)

Opening a nonexistent path in read-only mode raises FileNotFoundError.

File operations

file = open(file="data.txt", mode="w")
print("File name: %s" % file.name)
print("Mode: %s" % file.mode)
print("Status: %s" % file.closed)
print("Closing...")
file.close()
print("Status: %s" % file.closed)

Output

File name: data.txt
Mode: w
Status: False
Closing...
Status: True

Reading and Writing Files

After opening a file with open(), use the resulting file object to read and write.

A file opened for reading can be read line by line in a loop. Python also simplifies this: the file object itself is iterable, and each iteration reads one line separated by newline characters.

Method	Description
`close()`	Close the file resource
`fileno()`	Get the file descriptor
`flush()`	Force the buffer to flush
`read(n=-1)`	Read data; by default, read everything
`readlines(hint=-1)`	Read all data lines
`readline(size=-1)`	Read one line
`truncate(size=None)`	Truncate the file
`writable()`	Check whether writing is allowed
`write(s)`	Write to the file
`writelines(lines)`	Write a sequence of strings

Reading a file

with open(file="data.txt", mode="r", encoding="utf-8") as file:
	for line in file:
		print(line, end='')

data.txt

Alice 16
Bob 17
Terry 21

Output

Alice 16
Bob 17
Terry 21

Writing a file

with open(file="data.txt", mode="w", encoding="utf-8") as file:
	info = {"Alice": 16, "Bob": 17, "Terry": 21}
	for name, age in info.items():
		file.write("%s %d\n" % (name, age))

Output: data.txt

Alice 16
Bob 17
Terry 21

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QUESTION

data.txt already exists. Which mode erases its old content on opening?

QUESTION

After leaving with open(...) as file, what is file.closed?

TEXT

Maya 19
Noah 16
Iris 22

File Operations

File Operations

Opening a File

Reading and Writing Files

A file, a cursor and five opening modes

KNOWLEDGE QUIZ

KNOWLEDGE QUIZ

Read, select and append a summary

File Operations

File Operations

Opening a File

Reading and Writing Files

A file, a cursor and five opening modes

KNOWLEDGE QUIZ

KNOWLEDGE QUIZ

Read, select and append a summary