Comprehensive Guide to Python File Operations, CSV, JSON, and Pickle

1. Opening and Closing Files

The built‑in open() function opens a file and returns a file handle (e.g., f1 ). Parameters include the file path, mode (default 'r' ), and encoding (default OS encoding). Always close the handle with f1.close() or use with open() as f to auto‑close.

<code>f1 = open(r'd:\测试文件.txt', mode='r', encoding='utf-8')
content = f1.read()
print(content)
f1.close()</code>

<code>with open(r'd:\测试文件.txt', mode='r', encoding='utf-8') as f1:
    content = f1.read()
    print(content)</code>

Advantages of with open()

1) No need to manually close the file. 2) Multiple file handles can be managed in a single statement.

2. Absolute and Relative Paths

Absolute paths specify the full location (e.g., C:/Users/chris/.../python.exe ). Relative paths start from the current directory ( test.txt , ./test.txt , ../test.txt , demo/test.txt ).

3. Common File Access Modes

Text modes: r (read), w (write, truncates), a (append). Binary modes: rb , wb , ab . Combined modes with + allow read/write.

4. Reading and Writing Files

Reading

Methods include read() , read(n) , readline() , readlines() , and iteration over the file object.

<code>f1 = open('文件操作的读', encoding='utf-8')
content = f1.read()
print(content, type(content))
f1.close()</code>

Writing

Use write() with modes w (text) or wb (binary). The file is created if it does not exist; existing files are truncated.

<code>f1 = open('文件操作的写', encoding='utf-8', mode='w')
f1.write('lucy真帅')
f1.close()</code>

Pointer Positioning

tell() returns the current offset; seek(offset, whence) moves the pointer (whence: 0‑start, 1‑current, 2‑end).

<code>f = open('test.txt', 'rb')
print(f.read(3))
print(f.tell())
f.seek(2, 0)
print(f.read())
f.close()</code>

5. File Copying

Read a source file in binary chunks and write to a new file with a .bak suffix.

<code>import os
file_name = input('请输入一个文件路径:')
if os.path.isfile(file_name):
    old_file = open(file_name, 'rb')
    names = os.path.splitext(file_name)
    new_file_name = names[0] + '.bak' + names[1]
    new_file = open(new_file_name, 'wb')
    while True:
        content = old_file.read(1024)
        new_file.write(content)
        if not content:
            break
    new_file.close()
    old_file.close()
else:
    print('您输入的文件不存在')
</code>

6. CSV Reading and Writing

CSV files store tabular data as plain text. Use the csv module to read/write rows.

<code>import csv
file = open('test.csv', 'w')
writer = csv.writer(file)
writer.writerow(['name', 'age', 'score'])
writer.writerows([
    ['zhangsan', '18', '98'],
    ['lisi', '20', '99'],
    ['wangwu', '17', '90'],
    ['jerry', '19', '95']
])
file.close()
</code>

<code>import csv
file = open('test.csv', 'r')
reader = csv.reader(file)
for row in reader:
    print(row)
file.close()
</code>

7. In‑Memory Streams

StringIO handles text streams; BytesIO handles binary streams.

<code>from io import StringIO
f = StringIO()
f.write('hello\r\n')
f.write('good')
print(f.getvalue())
f.close()
</code>

<code>from io import BytesIO
f = BytesIO()
f.write('你好\r\n'.encode('utf-8'))
f.write('中国'.encode('utf-8'))
print(f.getvalue())
f.close()
</code>

8. Serialization with JSON and pickle

JSON

Use json.dumps() to get a string, json.dump() to write directly to a file, json.loads() to parse a string, and json.load() to read from a file.

<code>import json
names = ['zhangsan', 'lisi', 'wangwu']
result = json.dumps(names)
file = open('names.txt', 'w')
file.write(result)
file.close()
</code>

pickle

Pickle serializes Python objects to binary. Use pickle.dumps() or pickle.dump() for serialization, and pickle.loads() or pickle.load() for deserialization.

<code>import pickle
names = ['张三', '李四']
b_names = pickle.dumps(names)
file = open('names.txt', 'wb')
file.write(b_names)
file.close()
</code>

JSON is platform‑independent and human‑readable, while pickle is Python‑specific and preserves full object state.