Python read file
last modified January 29, 2024
Python read file tutorial shows how to read files in Python. We show several examples that read text and binary files.
If we want to read a file, we need to open it first. For this, Python has the
built-in open function.
Python open function
The open function is used to open files in Python.
open(file, mode='r', buffering=-1, encoding=None, errors=None, newline=None)
The file is the name of the file to be opened. The
mode indicates how the file is going to be opened: for reading,
writing, or appending. The buffering is an optional integer used to
set the buffering policy. The encoding is the name of the encoding
used to decode or encode the file. The errors is an optional string
that specifies how encoding and decoding errors are to be handled. The
newline controls the behaviour of the newline character.
The file modes are:
| Mode | Meaning |
|---|---|
| 'r' | open for reading (default) |
| 'w' | open for writing, truncating the file first |
| 'a' | open for writing, appending to the end of the file if it exists |
| 'b' | binary mode |
| 't' | text mode (default) |
| '+' | updating (reading and writing) |
| 'x' | exclusive creation, failing if file exists |
First, we deal with text files. At the end of the tutorial, we work with a binary file.
Lost Illusions Beatrix Honorine The firm of Nucingen Old Goriot Colonel Chabert Cousin Bette Gobseck César Birotteau The Chouans
We use this file for reading text.
Python read
The read function reads at most size characters as a
single string. If the size parameter is negative, it reads until
EOF.
#!/usr/bin/python
with open('works.txt', 'r') as f:
contents = f.read()
print(contents)
The example reads the whole file and prints its contents.
with open('works.txt', 'r') as f:
We open the works.txt file in the read mode. Since we did not specify
the binary mode, the file is opened in the default text mode. It returns the
file object f. The with statement simplifies exception
handling by encapsulating common preparation and cleanup tasks. It also
automatically closes the opened file.
contents = f.read()
We call the file object's read function. Since we did not specify
any parameter, it reads the whole file.
$ ./read_all.py Lost Illusions Beatrix Honorine The firm of Nucingen Old Goriot Colonel Chabert Cousin Bette Gobseck César Birotteau The Chouans
Python read characters
By providing the size parameter to the read function,
we can specify how many characters we want to read.
#!/usr/bin/python
with open('works.txt', 'r') as f:
data1 = f.read(4)
print(data1)
data2 = f.read(20)
print(data2)
data3 = f.read(10)
print(data3)
In the example, we read 4, 20, and 10 characters from the file.
$ ./read_characters.py
Lost
Illusions
Beatrix
H
onorine
Th
Python readline
The readline function reads until newline or EOF and return a
single string. If the stream is already at EOF, an empty string is returned. If
the size parameter is specified, at most size characters will be
read.
#!/usr/bin/python
with open('works.txt', 'r') as f:
line = f.readline()
print(line.rstrip())
line2 = f.readline()
print(line2.rstrip())
line3 = f.readline()
print(line3.rstrip())
In the example, we read three lines from the file. The rstrip
function cuts the trailing newline character from the string.
$ ./read_line.py Lost Illusions Beatrix Honorine
Python readlines
The readlines function reads and returns a list of lines from the
stream.
#!/usr/bin/python
with open('works.txt', 'r') as f:
lines = f.readlines()
print(lines)
for line in lines:
print(line.strip())
In the example, we read the contents of the file with readlines.
We print the list of the lines and then loop over the list with a for statement.
$ ./read_lines.py ['Lost Illusions\n', 'Beatrix\n', 'Honorine\n', 'The firm of Nucingen\n', 'Old Goriot\n', 'Colonel Chabert\n', 'Cousin Bette\n', 'Gobseck\n', 'César Birotteau\n', 'The Chouans\n'] Lost Illusions Beatrix Honorine The firm of Nucingen Old Goriot Colonel Chabert Cousin Bette Gobseck César Birotteau The Chouans
Python read file
Since the file object returned from the open function is a
iterable, we can pass it directly to the for statement.
#!/usr/bin/python
with open('works.txt', 'r') as f:
for line in f:
print(line.rstrip())
The example iterates over the file object to print the contents of the text file.
$ ./read_file.py Lost Illusions Beatrix Honorine The firm of Nucingen Old Goriot Colonel Chabert Cousin Bette Gobseck César Birotteau The Chouans
The seek function
The seek function changes the stream position to the given byte offset.
The offset value is interpreted relative to the position indicated
by whence. The default value for whence is SEEK_SET.
The values for whence are:
SEEK_SETor 0 – start of the stream (the default); offset should be zero or positiveSEEK_CURor 1 – current stream position; offset may be negativeSEEK_ENDor 2 – end of the stream; offset is usually negative
#!/usr/bin/python
with open('works.txt', 'r') as f:
data1 = f.read(22)
print(data1)
f.seek(0, 0)
data2 = f.read(22)
print(data2)
In the example, we read 22 characters from a text stream. Then we set the stream position back to the beginning and read 22 characters again.
$ ./seeking.py Lost Illusions Beatrix Lost Illusions Beatrix
The tell function
The tell function returns the current stream position.
#!/usr/bin/python
with open('works.txt', 'r') as f:
print(f'The current file position is {f.tell()}')
f.read(22)
print(f'The current file position is {f.tell()}')
f.seek(0, 0)
print(f'The current file position is {f.tell()}')
We move the stream position with read and seek
and print it with tell.
$ ./telling.py The current file position is 0 The current file position is 22 The current file position is 0
Python read file with try/except/finally
The with statement simplifies our work when reading files.
Without with, we need to manually handle exceptions and close
the resources.
#!/usr/bin/python
f = None
try:
f = open('works.txt', 'r')
for line in f:
print(line.rstrip())
except IOError as e:
print(e)
finally:
if f:
f.close()
In the example, we deal with the exceptions and resource release using
try, except, and finally keywords.
Python read binary file
In the following example, we read a binary file.
#!/usr/bin/python
with open('web.png', 'rb') as f:
hexdata = f.read().hex()
n = 2
data = [hexdata[i:i+n] for i in range(0, len(hexdata), n)]
i = 0
for e in data:
print(e, end=' ')
i += 1
if i % 20 == 0:
print()
print()
The example reads a PNG file. It outputs the data as hexadecimal values.
with open('web.png', 'rb') as f:
We open the PNG file in read and binary modes.
hexdata = f.read().hex()
We read all data and turn it into hexadecimal values with hex
function.
n = 2 data = [hexdata[i:i+n] for i in range(0, len(hexdata), n)]
We chunk the string into a list of two characters.
i = 0
for e in data:
print(e, end=' ')
i += 1
if i % 20 == 0:
print()
We print the data in columns; there is a space between the columns. There are 20 columns per line of output.
$ ./read_binary.py 89 50 4e 47 0d 0a 1a 0a 00 00 00 0d 49 48 44 52 00 00 00 10 00 00 00 10 08 06 00 00 00 1f f3 ff 61 00 00 03 2a 49 44 41 54 78 01 75 53 43 98 23 69 18 ae eb 7a af eb 4a c6 b6 ed 38 19 bb b5 6c db 66 55 45 dd 71 66 9f a4 ad 8a 9d b1 6d e3 fe ac 77 2f 63 bf 5b 55 a7 e1 e1 c7 a7 f7 33 01 e0 b5 43 6a 1a 3e 27 e5 6d a9 62 b9 d6 39 4a a5 bd 3e 4a ad bb 22 56 d2 76 ...
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In this article we have showed how to read files in Python.
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