Data Input and Output

  • Reading and Writing Data from/to Different Formats (CSV, Excel, SQL, JSON, etc.)
  • Web Scraping with Pandas

How to Read and Write Data in Fixed-Width Format in Pandas

Pandas provides the read_fwf() function to efficiently read data from fixed-width formatted files. These files, unlike comma-separated value (CSV) files, organize data by assigning a specific number of characters to each column. This consistent width allows for structured data storage without delimiters.

The core function for reading these files is pandas.read_fwf(). A critical parameter is filepath_or_buffer, which specifies the path to your fixed-width file. Equally important is colspecs, which defines the starting and ending positions of each column. You can provide a list of tuples, where each tuple represents a column’s start and end indices. Alternatively, you can use ‘infer’, allowing Pandas to attempt to deduce column widths from the file’s content. If you prefer, widths can be used to specify the width of each column, which is more convenient when the columns are contiguous. The delimiter parameter can be used to define filler characters, if the file uses characters other than spaces. The dtype parameter works the same as with other pandas read functions, and allows you to specify the datatypes of the columns. (more…)

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How to Create Custom Parsers for Complex Text Files in Pandas

Pandas excels at handling structured data, but sometimes you encounter complex text files that don’t fit standard formats like CSV or fixed-width. In such cases, creating custom parsers becomes essential. These parsers allow you to extract data from files with irregular structures, log files, or other non-standard formats.

The core approach involves using Python’s file handling capabilities in conjunction with string manipulation and regular expressions. You would typically read the file line by line or in chunks, then apply custom logic to extract the desired data. Pandas can then be used to construct DataFrames from the parsed data.

For instance, imagine a log file where each line has a timestamp, a message type, and a message, but the format varies. You could read the file line by line, use regular expressions to extract the components, and store them in lists. These lists can then be used to create a Pandas DataFrame. (more…)

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How to Specify Data Types During CSV Import in Pandas

When importing CSV files into Pandas DataFrames, it’s vital to specify data types to ensure data integrity and optimize performance. Pandas’ read_csv() function offers the dtype parameter to achieve this. Specifying data types is important because Pandas attempts to infer data types, but can sometimes make incorrect assumptions. For example, a column with numerical IDs might be interpreted as integers or strings, leading to unexpected behavior. Specifying data types guarantees your data is interpreted correctly. Furthermore, specifying data types can significantly improve memory usage and processing speed, especially with large datasets. Finally, it ensures data consistency across different analyses and operations. (more…)

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