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python pandas to_sql example

First install pandas, sqlalchemy and corresponding database drivers; 2. Create DataFrame data; 3. Use sqlalchemy.create_engine to establish a database connection; 4. Call the df.to_sql method to specify the table name, connection object, if_exists policy, whether to write index, chunk size and insert method, and the data can be written to the database, and the data has been successfully written to the SQLite database!

Jul 29, 2025 am 12:03 AM

Python Pandas Merge_asof Example

pandas.merge_asof() is used for approximate merge of time series, 1. Use on to specify the time column for alignment, 2. Specify the grouping key (such as stock code) by, 3. Set the direction to control the matching direction ('backward' takes the most recent value that does not advance), 4. Optional tolerance limits the matching time range, 5. The input data must be sorted in column on, and finally achieve the left-joined approximate matching, all left-side data are retained, and NaN is filled if it does not match.

Jul 28, 2025 am 03:25 AM

python pandas resample time series example

resample() is the core method used in Pandas for time series resampling, which can group and aggregate data by specified time frequency. 1. It is similar to groupby(), but is specifically used for time series. It is necessary to ensure that the index is DatetimeIndex; 2. Downsampling (such as minutes to hour) uses frequency codes such as 'H' and 'D' combined with aggregate functions such as mean() and sum(), such as df.resample('H').mean() to calculate the average hourly; 3. Upsampling (such as hour to minute) will produce missing values, which need to be filled with ffill() or bfill(); 4. Supports multiple frequencies such as 'T' (minute), '5T' (5 minutes), and 'W' (weeks

Jul 28, 2025 am 03:23 AM

sequentially pandas

Optimizing Python for Memory-Bound Operations

Pythoncanbeoptimizedformemory-boundoperationsbyreducingoverheadthroughgenerators,efficientdatastructures,andmanagingobjectlifetimes.First,usegeneratorsinsteadofliststoprocesslargedatasetsoneitematatime,avoidingloadingeverythingintomemory.Second,choos

Jul 28, 2025 am 03:22 AM

python Memory optimization

python stack example

In Python, you can use list to implement the stack. 1. Use append() to press the stack, 2. Use pop() to pop the stack, 3. View the top of the stack through the index [-1], 4. Use len() to determine whether it is empty, 5. Encapsulating the Stack class can improve the readability of the code. All operations are based on the end to ensure the O(1) time complexity, and are suitable for function calls, bracket matching, DFS, undo operations and other scenarios.

Jul 28, 2025 am 03:12 AM

python shutil move file example

shutil.move() is a common method used in Python to move files and directories, and supports cross-platform operations. 1. Move a single file: Use shutil.move(src,dst) to move the file from the source path to the target path; 2. Move to the directory and retain the original name: If dst is an existing directory, the file will be placed in the directory with its original name; 3. Move and rename: specify dst as the new file name to achieve movement and renaming at the same time; 4. Move the entire directory: supports moving non-empty folders; 5. Notes: The target parent directory must exist, otherwise it must be created with os.makedirs() first, and the target file may be overwritten or errors may be reported. It is recommended to check in advance; 6. Complete security example: Confirm first

Jul 28, 2025 am 03:10 AM

python psycopg2 connection pool example

Use psycopg2.pool.SimpleConnectionPool to effectively manage database connections and avoid the performance overhead caused by frequent connection creation and destruction. 1. When creating a connection pool, specify the minimum and maximum number of connections and database connection parameters to ensure that the connection pool is initialized successfully; 2. Get the connection through getconn(), and use putconn() to return the connection to the pool after executing the database operation. Constantly call conn.close() is prohibited; 3. SimpleConnectionPool is thread-safe and is suitable for multi-threaded environments; 4. It is recommended to implement a context manager in combination with context manager to ensure that the connection can be returned correctly when exceptions are noted;

Jul 28, 2025 am 03:01 AM

python Psycopg2

python ternary operator example

Python's ternary operator is used to concisely implement if-else judgment, and its syntax is "value_if_trueif conditionelsevalue_if_false"; 1. It can be used for simple assignment, such as returning the corresponding string based on positive and negative values; 2. It can avoid division errors, such as determining that the denominator is non-zero and then division; 3. It can select content according to conditions in string format; 4. It can assign labels to different elements in list derivation formula; it should be noted that this operator is only suitable for binary branches and should not be nested multiple layers. Complex logic should use the traditional if-elif-else structure to ensure readability.

Jul 28, 2025 am 02:57 AM

java programming

python list sort vs sorted example

list.sort() directly modify the original list and returns None, which is suitable for scenarios where there is no need to retain the original order and pursue memory efficiency; 2.sorted() does not change the original list and returns a new list, which is suitable for scenarios where original data needs to be retained or non-list iterable objects are processed; 3. Both support reverse and key parameters for customized sorting. When selecting, which method should be used based on whether the original data needs to be retained and the input type.

Jul 28, 2025 am 02:57 AM

python sort

Network Programming Essentials in Python Sockets

Python socket programming is the basis of network communication. The article introduces common usage and precautions for TCP server, client and UDP communication. 1. TCP server steps: create socket, bind address, listen to connection, accept requests and process data; 2. TCP client process: create socket, connect to server, send data, and receive responses, and exception processing is required; 3. UDP communication uses SOCK_DGRAM type, no connection is required, sendto and recvfrom directly; 4. Common problems include sticking packets, blocking, connection closure and cross-platform compatibility, and need to define message boundaries, handle blocking mode reasonably, close connections in time, and pay attention to platform differences. Master these key points and write

Jul 28, 2025 am 02:57 AM

python signal handling python example

When processing signals in Python, you need to use the signal module to register a custom processing function. First, bind SIGINT and SIGTERM signals through signal.signal(). 1. Define the global running flag bit to control the main loop; 2. Write a signal processing function to capture the signal and set running to False; 3. Check the running status regularly in the main loop to achieve elegant exit; 4. Resources can be released, logs, etc. before the program exits; note that the signal is only effective in the main thread, and the processing function should avoid complex operations and cannot capture SIGKILL and SIGSTOP. In the end, the program can terminate safely in response to Ctrl C or kill commands.

Jul 28, 2025 am 02:55 AM

python signal processing

python check if item is in list example

The easiest way to check whether an element is in a list is to use the in keyword. 1. Use the in operator to directly determine whether the element exists. For example, itemmy_list will return True or False; 2. The same applies when checking the string, such as 'banana'infruits; 3. Use notin to determine whether the element does not exist; 4. Pay attention to the time complexity of in. It is recommended to convert it to set for O(1) search; 5. Pay attention to data type and case sensitivity issues when comparing; 6. If you need to obtain the index, you should first use in to judge the existence and then call the index() method, or use try-except to handle exceptions; this method is suitable for all types of lists and is the most straightforward

Jul 28, 2025 am 02:53 AM

java programming

python pytest example

First install pytest: pipinstallpytest; 2. Write the added and divide functions of the code under test; 3. Write the test file to include normal tests, exception tests and parameterized tests; 4. Use the pytest-v command to run the test; 5. Optionally install pytest-cov to view the test coverage. This example fully demonstrates the basic usage of pytest, which is suitable for beginners to quickly get started and understand the testing process.

Jul 28, 2025 am 02:48 AM

java programming

How to check if a file exists in Python

Check if the file exists for available os or pathlib modules. 1. Use os.path.exists() to determine whether the path exists, and os.path.isfile() to determine whether it is a file; 2. Use pathlib's Path().exists() and Path().is_file() methods to be more modern and clear; 3. It is recommended to directly try to open the file and use try-except to handle exceptions to avoid race conditions. The three methods have their own applicable scenarios, and the choice depends on the code style and Python version.

Jul 28, 2025 am 02:44 AM