python read file line by line example
The recommended way to read files line by line in Python is to use with open() and for loops. 1. Use with open('example.txt', 'r', encoding='utf-8') as file: to ensure safe closing of the file; 2. Use for line in file: to realize line-by-line reading, memory-friendly; 3. Use line.strip() to remove line-breaks and whitespace characters; 4. Specify encoding='utf-8' to prevent encoding errors; other techniques include skipping blank lines, reading N lines before, getting line numbers and processing lines according to conditions, and always avoiding manual opening without closing. This method is complete and efficient, suitable for large file processing, and is recommended for use in actual projects.
Reading files line by line in Python is a very common operation and is often used to process log files, configuration files, or large amounts of text data. Here is a simple and practical example showing how to read files line by line.
✅ Recommended method: use with open() and for loop
with open('example.txt', 'r', encoding='utf-8') as file:
for line in file:
line = line.strip() # Remove the beginning and end whitespace characters (such as line breaks)
print(line)illustrate:
-
with open()ensures that the file is automatically closed after use, and is safe even if an exception occurs. -
encoding='utf-8'avoid encoding errors in Chinese or special characters (adjust according to actual conditions). -
line.strip()removes the\nor\r\nline breaks at the end of each line, as well as extra spaces.
? Other common scenarios and techniques
1. Skip empty lines while reading
with open('example.txt', 'r', encoding='utf-8') as file:
for line in file:
line = line.strip()
if not line: # Skip the blank line continue
print(line)2. Read only the first N lines (such as the first 5 lines)
from itertools import islice
with open('example.txt', 'r', encoding='utf-8') as file:
for line in islice(file, 5): # read the first 5 lines print(line.strip())3. Get the line number (with numbered output)
with open('example.txt', 'r', encoding='utf-8') as file:
for lineno, line in enumerate(file, 1):
print(f"{lineno}: {line.strip()}")4. Process certain lines according to conditions (such as lines containing keywords)
with open('example.txt', 'r', encoding='utf-8') as file:
for line in file:
if 'error' in line.lower():
print("Error line found:", line.strip())⚠️ Not recommended (prone to problems)
# ❌ Not recommended: Manually open but forget to close
file = open('example.txt', 'r')
for line in file:
print(line.strip())
file.close() # If an error occurred before, this sentence may not be executedAlways give priority to using the
withcontext manager.
✅ Summary: Key points
- ✅ Use
with open()to safely read files - ✅ Use
for line in file:read line by line, memory friendly (suitable for large files) - ✅ Add
strip()to remove unnecessary line breaks and spaces - ✅ Specify
encodingto prevent garbled code (especially in Windows environments)
Basically that's it. Not complicated, but it is easy to ignore details.
The above is the detailed content of python read file line by line example. For more information, please follow other related articles on the PHP Chinese website!
Hot AI Tools
Undress AI Tool
Undress images for free
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
How to create a virtual environment in Python
Aug 05, 2025 pm 01:05 PM
To create a Python virtual environment, you can use the venv module. The steps are: 1. Enter the project directory to execute the python-mvenvenv environment to create the environment; 2. Use sourceenv/bin/activate to Mac/Linux and env\Scripts\activate to Windows; 3. Use the pipinstall installation package, pipfreeze>requirements.txt to export dependencies; 4. Be careful to avoid submitting the virtual environment to Git, and confirm that it is in the correct environment during installation. Virtual environments can isolate project dependencies to prevent conflicts, especially suitable for multi-project development, and editors such as PyCharm or VSCode are also
python schedule library example
Aug 04, 2025 am 10:33 AM
Use the Pythonschedule library to easily implement timing tasks. First, install the library through pipinstallschedule, then import the schedule and time modules, define the functions that need to be executed regularly, then use schedule.every() to set the time interval and bind the task function. Finally, call schedule.run_pending() and time.sleep(1) in a while loop to continuously run the task; for example, if you execute a task every 10 seconds, you can write it as schedule.every(10).seconds.do(job), which supports scheduling by minutes, hours, days, weeks, etc., and you can also specify specific tasks.
How to run Python code in Sublime Text
Aug 04, 2025 pm 04:25 PM
EnsurePythonisinstalledandaddedtoPATHbycheckingversioninterminal;2.Savefilewith.pyextension;3.UseCtrl Btorunviadefaultbuildsystem;4.CreateacustombuildsystemifneededbygoingtoTools>BuildSystem>NewBuildSystem,enteringthecorrectcmdforyourPythonvers
What are common strategies for debugging a memory leak in Python?
Aug 06, 2025 pm 01:43 PM
Usetracemalloctotrackmemoryallocationsandidentifyhigh-memorylines;2.Monitorobjectcountswithgcandobjgraphtodetectgrowingobjecttypes;3.Inspectreferencecyclesandlong-livedreferencesusingobjgraph.show_backrefsandcheckforuncollectedcycles;4.Usememory_prof
How to work with timezones in Python?
Aug 05, 2025 pm 04:53 PM
UsezoneinfoforPython3.9 tocreatetimezone-awaredatetimesandconvertbetweentimezoneswithastimezone();2.ForPython3.6–3.8,usepytzwithlocalize()toavoidDSTerrors;3.AlwaysworkinUTCinternallyandconverttolocaltimeonlyfordisplay;4.Parsetimezone-awarestringsusin
Java vs Python for Backend Development: A Detailed Comparison
Aug 04, 2025 am 11:57 AM
Systems with high performance requirements, such as Java for financial transactions, Python for lightweight services; 2. Python has high development efficiency, suitable for MVP, Java is suitable for large-scale team collaboration; 3. Java is mature in the Java enterprise-level ecosystem, and the Python framework is light, especially FastAPI is outstanding; 4. Java is the first choice for high-concurrency distributed systems, and Python requires asynchronous models to improve performance; 5. Python has a smooth learning curve, and a wide range of talents, and Java has sufficient reserves of enterprise-level talents; 6. Python is suitable for cloud-native lightweight deployment, and Java is more stable in traditional operation and maintenance; the final choice should be combined with the team's technology stack, project cycle, performance requirements, integration complexity and operation and maintenance costs, and the key is to use the right scenario.
python flask blueprint example
Aug 05, 2025 am 01:44 AM
Use FlaskBlueprint to modularize the application according to functions; 1. Create blueprint instances and define routes, such as creating user_bp in user.py; 2. Create other blueprints in another file such as post.py; 3. Import in app.py and register each blueprint with app.register_blueprint(); 4. After running, access the corresponding URL to see the modular routing effect, the code structure is clearer and easy to maintain.
How to automate data entry from Excel to a web form with Python?
Aug 12, 2025 am 02:39 AM
The method of filling Excel data into web forms using Python is: first use pandas to read Excel data, and then use Selenium to control the browser to automatically fill and submit the form; the specific steps include installing pandas, openpyxl and Selenium libraries, downloading the corresponding browser driver, using pandas to read Name, Email, Phone and other fields in the data.xlsx file, launching the browser through Selenium to open the target web page, locate the form elements and fill in the data line by line, using WebDriverWait to process dynamic loading content, add exception processing and delay to ensure stability, and finally submit the form and process all data lines in a loop.
