103 lines
3.1 KiB
Markdown
103 lines
3.1 KiB
Markdown
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---
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tags: [python, file-system, procedural]
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created: Friday, October 25, 2024
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---
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# Reading files in Python
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Once a file object has been intialised with `open()` there are several ways in
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which the content can be read:
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| Read method | Behaviour |
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| ----------- | ---------------------------------------------------------------------------------------------------------------------------------------- |
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| `read` | Return the entire contents of the file as a single string. |
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| `readline` | Read the contents of a file a line at a time. You would combine this with a loop so that you can do something with each individual line. |
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| `readlines` | Return a list of all the lines in a file. Each line will be an element in the list. |
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## Read
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`read` reads the entire contents of a file and returns it as a single string.
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`read()` reads the entire file into memory at once, so it may not be suitable
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for very large files that exceed the available memory of your system. In such
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cases, you can use the `readline()` method to read the file line by line
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instead.
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The basic syntax is as follows:
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```py
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# Open the file for reading
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file = open('filename.txt', 'r')
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# Read the entire contents of the file
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contents = file.read()
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# We could also limit the read to a number of characters:
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contents = file.read(100)
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# Close the file
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file.close()
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```
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Once we have the file contents stored, we can then interact with it. The
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standard way of doing this is to parse it line by line. For example, say we were
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reading a CSV:
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```py
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lines = content.split(',')
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for line in lines:
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if line: # if the line is not empty
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# do something with line
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```
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## Readline
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> The readline() method in Python is used to read a single line from a file. It
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> is typically used when you want to process a file line by line, rather than
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> reading the entire file into memory at once.
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`readline()` returns the line including the newline character at the end of the
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line, so you may need to strip this character off using the strip() method
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before processing the line further.
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```python
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# Open the file for reading
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file = open('filename.txt', 'r')
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# Loop through the file, reading one line at a time
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line = file.readline()
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while line:
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# Strip off the newline character
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line = line.strip()
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# Do something with the line
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print(line)
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# Read the next line
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line = file.readline()
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# Close the file
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file.close()
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```
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## Readlines
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The `readlines()` method is used to read all the lines of a file and return them
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as a list of strings, where each element of the list is a line from the file.
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```py
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# Open the file for reading
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file = open('filename.txt', 'r')
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# Read all the lines of the file and store them in a list
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lines = file.readlines()
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# Loop through the lines and print them to the console
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for line in lines:
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print(line)
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# Close the file
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file.close()
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`
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```
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