Use the else block

Write a Python program that uses else to run code only when no exception occurred.

"25", "x"

25 squared is 625
x is not a number

Approach

1. else runs after try only if nothing was raised.

Solution

for text in ["25", "x"]:    try:        n = int(text)    except ValueError:        print(text, "is not a number")    else:        print(text, "squared is", n * n)

25 squared is 625
x is not a number

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Use the finally block

Write a Python program that shows finally always runs.

  result: 25.0
  clean-up done
  error handled
  clean-up done

Approach

1. Run the function once successfully and once with an error.

Solution

def process(value):    try:        print("  result:", 100 / value)    except ZeroDivisionError:        print("  error handled")    finally:        print("  clean-up done") process(4)process(0)

  result: 25.0
  clean-up done
  error handled
  clean-up done

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Handle a missing dictionary key

Write a Python program that reads a key from a dictionary and handles a missing key.

missing key: 'timeout'
30

Approach

1. Catch KeyError; compare with dict.get().

Solution

config = {"browser": "chromium"}try:    print(config["timeout"])except KeyError as e:    print("missing key:", e)print(config.get("timeout", 30))

missing key: 'timeout'
30

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Handle division by zero

Write a Python program that divides two numbers and prints a friendly message when the divisor is 0.

(10, 2), (5, 0)

5.0 | cannot divide by zero

Approach

1. Put the division in try and catch ZeroDivisionError.

Solution

def safe_divide(a, b):    try:        return a / b    except ZeroDivisionError:        return "cannot divide by zero" print(safe_divide(10, 2), "|", safe_divide(5, 0))

5.0 | cannot divide by zero

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Handle invalid integer input

Write a Python program that converts text to an integer and reports invalid values.

"42", "4.2", "abc"

42 -> 42
4.2 -> invalid: invalid literal for int() with base 10: '4.2'
abc -> invalid: invalid literal for int() with base 10: 'abc'

Approach

1. int() raises ValueError for text that is not a whole number.

Solution

for text in ["42", "4.2", "abc"]:    try:        print(text, "->", int(text))    except ValueError as e:        print(text, "-> invalid:", e)

42 -> 42
4.2 -> invalid: invalid literal for int() with base 10: '4.2'
abc -> invalid: invalid literal for int() with base 10: 'abc'

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Handle an index out of range

Write a Python program that reads a list item by index and handles invalid indexes.

index 1 and 10 of ["a", "b", "c"]

1 b
10 is out of range for 3 items

Approach

1. Catch IndexError.

Solution

items = ["a", "b", "c"]for i in [1, 10]:    try:        print(i, items[i])    except IndexError:        print(i, "is out of range for", len(items), "items")

1 b
10 is out of range for 3 items

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Platform information

Write a Python program to print platform details.

OS: Windows
Architecture bits: 64bit
Python implementation: CPython

Approach

1. The platform module.

Solution

import platform print("OS:", platform.system())print("Architecture bits:", platform.architecture()[0])print("Python implementation:", platform.python_implementation())

OS: Windows
Architecture bits: 64bit
Python implementation: CPython

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File details with os.stat()

Write a Python program to show the details of a file with os.stat().

size: 5
is regular file: True
has mtime: True

Approach

1. stat() returns size, timestamps and mode.

Solution

import osimport stat with open("info.txt", "w") as f:    f.write("hello")st = os.stat("info.txt")print("size:", st.st_size)print("is regular file:", stat.S_ISREG(st.st_mode))print("has mtime:", st.st_mtime > 0)

size: 5
is regular file: True
has mtime: True

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Does a path exist?

Write a Python program to check whether a path exists.

here.txt True
. True
nowhere False

Approach

1. os.path.exists works for files and folders.

Solution

import os open("here.txt", "w").close()for p in ["here.txt", ".", "nowhere"]:    print(p, os.path.exists(p))

here.txt True
. True
nowhere False

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Is a path a symbolic link?

Write a Python program to check whether a path is a symbolic link.

Creating symlinks needs extra permission here
target.txt is a link: False

Approach

1. os.path.islink; creating links may need extra rights on Windows, so handle the error.

Solution

import os open("target.txt", "w").close()try:    if not os.path.lexists("link.txt"):        os.symlink("target.txt", "link.txt")    print("link.txt is a link:", os.path.islink("link.txt"))except OSError:    print("Creating symlinks needs extra permission here")print("target.txt is a link:", os.path.islink("target.txt"))

Creating symlinks needs extra permission here
target.txt is a link: False

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