Document Operation in Python (Read)

In daily life the common operation to the documents will be:

• Open
• Close
• Read
• Write

open()

Usage

open(name, mode, encoding)

• Name: file path (with directory)
• Mode: Write, Read, ...
• Encoding: Normally document will encode with UTF-8

Info

• Position of encoding is not on 3, so can't use positional arguments, must using keywords arguments to define

'r'	open for reading (default)
'w'	open for writing, truncating the file first
'x'	create a new file and open it for writing
'a'	open for writing, appending to the end of the file if it exists
'b'	binary mode
't'	text mode (default)
'+'	open a disk file for updating (reading and writing)

Example

Step:

1. Create a file name "test.txt" at the root of the project that same with the python file

2. Define a variable name and open the test file, with the mode = read, and encoding of UTF-8

file-operation.py

file = open("./test.txt", "r", encoding="UTF-8")
print(type(file))

Output:

<class '_io.TextIOWrapper'>

read()

Step 3: Open test.txt file and write the data below:

test.txt

Hello
Hi
Hola
Ni Hao

Syntax

f.read(num)

• If num is not define, by default it will read entire file
• num means the length of the data read from a document (unit: byte)

Usage

print(file.read())

Output:

Hello
Hi
Hola
Ni Hao

Usage - with size

# If use directly will EOF (end of file), must comment file.read() first
print(file.read(5))

Output:

Hello

readlines()

• readlines() will read entire file and return a list, each line of data will be each element of the list.

Syntax

f.readlines()

Usage

# readlines
lines = file.readlines()

print(type(lines))
print(lines)

Output:

<class 'list'>
['Hello\n', 'Hi\n', 'Hola\n', 'Ni Hao']

readline()

• It only read 1 line at once (one call).

Syntax

f.readline() # Read 1st line
f.readline() # Read 2nd line

Usage

Print directly

# readline
print(file.readline()) # 1st line
print(file.readline()) # 2nd line

Output:

Hello

Hi

Using for to print all lines

# using for with readline
for line in file:
    print(line)

Output:

Hello

Hi

Hola

Ni Hao

close()

• Use to close the document.
• If the document is not close even the programme not using will cause the waste of resources.
• For most of the problem will be faced is the file cannot be deleted while the file is in use.

Example

import time

time.sleep(111111111) # Programme stop here until timer is gone
file.close()

with open() as f

• By using with open() can prevent us from forgotting put file.close().
• As after completed the file operation python will automatically close it.

Usage

with open("./test.txt") as f:
    line = f.readlines()
    print(line)

Output:

['Hello\n', 'Hi\n', 'Hola\n', 'Ni Hao']

Conclusion

Extra: Find the number of same element in a file

text2.txt

python js java
python python java
js c++ c
ruby react python

• Find number of times that python appeared.

file-operation-2.py

with open("./text2.txt", mode="r", encoding="UTF-8") as f:
    lines = f.readlines()
    number_of_python_appeared = int(0)

    for line in lines:
        number_of_python_appeared += line.count("python")

    print(f"Python appeared {number_of_python_appeared} times")

# or

with open("./text2.txt", mode="r", encoding="UTF-8") as f:

    number_of_python_appeared = int(0)

    for line in f:
        number_of_python_appeared += line.count("python")

    print(f"Python appeared {number_of_python_appeared} times")

Output:

Python appeared 4 times
Python appeared 4 times