Python - Tips & Hacks

Listing Outdate Packages in Python

Python3 comes with a list of pre-installed packages which are updated from time to time. It is really easy to list any outdated package with the following command:

pip list --outdated

# Output
Package    Version   Latest     Type
---------- --------- ---------- -----
astroid    2.0.4     2.1.0      wheel
certifi    2018.4.16 2018.11.29 wheel
pylint     2.1.1     2.2.2      wheel
setuptools 40.0.0    40.6.3     wheel
six        1.11.0    1.12.0     wheel

As you can see 5 packages on my machine are outdated.

To update a specific package to the latest version you can use

pip install --upgrade  <PackageName>

# Alternatively you can use the short form
pip install -U <PackageName>

In you don’t want to install each update individually you can use pipdate

# Install pipdate
sudo pip3 install pipdate

# Update all packages
sudo pipdate3

Note for Windows users: Pipdate is already installed by default so you don’t need to install it

Note for Mac users: If you installed Python via homebrew there is no need to use sudo to install pipdate or upgrade packages

File Navigations

This is something I used to stumble on a lot in the early days of my Python coding adventure so I thought to write a quick article about it.

Python Open file

Opening a file for read or write in Python can be achieved with the following code:

# Open file
file = open("/Python/Files/MyFile.txt")

Python Read file

To read content of the file we simply use the read() method

# Read file to the end of file
file.read()

'This is the first line\nAnd a second\nAnd even a third\nShall we put a fourth?\nWhy not a fifth\nOr a sixt\n'

Note that Python will print the newline character and will not split lines for you (but that’s material for another day/post)

Where is my text?

Say you want to print again file content issue the same command again will leave you with something like this

# Read file again
file.read()
''

Not a lot to see on screen, so where did our file’s content go?

Python seek()

When Python reads a file’s content it will move file current position to the end of the file so trying to re-read it again will yield the above result. Nothing as there is nothing else to read.

You can easily go back to the beginning of the file with the seek() method which is used like this:

# Go back to position 0
# Or beginning of file
file.seek(0, 0)

Syntax of seek() method - fileObject.seek(offset[, whence])
offset is the position of the read/write pointer within the file.
whence is optional and defaults to 0 which means absolute file positioning, other possible values are 1 which means seek relative to the current position and 2 which means seek relative to the file’s end

Now if you try to read the file again all content will be correctly displayed

file.read()

'This is the first line\nAnd a second\nAnd even a third\nShall we put a fourth?\nWhy not a fifth\nOr a sixt\n'

🔍How to Create Infinite Iteration using “itertools.cycle”

Use-cases?

👉Round-robin task scheduling.

👉Creating repeating patterns in data processing.

👉Continuously cycling through a list of configurations or parameters.

The itertools.cycle function can be used to iterate over a sequence infinitely.

👉 itertools.cycle: Takes an iterable and returns an iterator that produces the elements of the iterable in a cycle, repeating indefinitely.

👉 next: Used to get the next item from the iterator.

import itertools

# Define a list of values
colours = ['red', 'green', 'blue']

# Create an infinite iterator
infinite_colors = itertools.cycle(colours)

# Use the iterator
for _ in range(10):
    print(next(infinite_colors))

Immutable & Mutable classes in Python using data class

Data Classes in Python are a Huge saver for boilerplate code. There could be instances where your Python classes may need to be defined as an immutable object. The “frozen” parameter is of help here.

from dataclasses import dataclass

# Not Immutable 

@dataclass()
class Point:
    x: int
    y: int

# Create an instance of the data class
point = Point(x=1, y=2)

print(point)  # Output: Point(x=1, y=2)

# Attempting to modify the fields will NOT raise an error
try:
    point.x = 10
except AttributeError as e:
    print(e) 

print(point)  # Output: Point(x=10, y=2)

# Freezing the Class, thereby becoming Immutable.

from dataclasses import dataclass

@dataclass(frozen=True)
class Point:
    x: int
    y: int

# Create an instance of the data class
point = Point(x=1, y=2)

print(point)  # Output: Point(x=1, y=2)

# Attempting to modify the fields will raise an error
try:
    point.x = 10
except AttributeError as e:
    print(e)  # Output: cannot assign to field 'x'

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