Python
Requirements
# Get the requirments to a file
pip freeze -r myrequiremets.txt
# Installing the modules from the requirments file
pip install -r myrequirements.txt
Preventing user input during sleep.
This function disables all user input if used after a sleep function. As this uses the msvcrt module, this is only usable on Microsoft Windows.
import msvcrt
def disableInput():
while msvcrt.kbhit(): msvcrt.getwch()
#example usage
time.sleep(5)
disableInput()
input("Press enter to continue...")
Python 3 f-strings: formatted string literals
The new f-Strings are string literals that start with an f at the beginning, and allow for expressions to be evaluated inside of curly braces. This is way easier to keep track of, especially with a long set of parameters and strings.
Simple Syntax
name = "Sal"
age = 33
f"Hello, {name}. You are {age}"
# 'Hello, Sal. You are 33.'
# Capital `F` is also valid
F"Hello, {name}. You are {age}"
# 'Hello, Sal. You are 33.'
# The output returned is a string, with single quotes, but you can wrap f-Strings in the print command, too.
print(f"{name} is {age} and that is great!")
# Sal is 33 and that is great!
Arbitrary Expressions
Since f-Strings are evaluated at runtime, you can put any valid Python expression inside of them. This allows for some cool things to happen!
# The basics
f"{2 * 21}"
# '42'
# You can call functions
def to_lowercase(input):
return input.lower()
name = "Sal Mac"
f"{to_lowercase(name)} loves to code."
# 'sal mac loves to code.'
Two Matrix Multiplication
The following python snippet is for multiplication of two matrix. simply using for loops & list.
r1 = int(input("Enter no. of rows of first matrix : "))
c1 = int(input("Enter no. of columns of first matrix : "))
r2 = int(input("Enter no. of rows of second matrix : "))
c2 = int(input("Enter no. of columns of second matrix : "))
C = []
D = []
A = []
print("\nFirst Matrix :")
for i in range(r1):
temp1 = []
for i in range(c1):
temp1.append(float(input("Enter a value : "))) #values of first matrix
A.append(temp1)
B = []
print("\nSecond Matrix :")
for i in range(r2):
temp2 = []
for i in range(c2):
temp2.append(float(input("Enter a value : "))) #values of second matrix
B.append(temp2)
print("\nFirst Matrix : ",A)
print("Second Matrix : ",B)
for i in range(r1):
for j in range(c2):
s= 0
for k in range(c1):
s = s+(A[i][k]*B[k][j]) # perform matrix multiplication
C.append(s)
D.append(C)
C = []
print("\nFinal Matrix : ",D) # final matrix after multiplication
Useful Function - Force 2 Decimals
This function returns the given integer as a string with 2 decimals points, useful for prices.
def forceTwoDecimals(integer):
if str(round(integer,2)) == str(round(integer,1)):
return str(integer)+"0"
else:
return str(integer)
Useful Function - isPalindrome
This function returns true if a given string is a palindrome
def isPalindrome(str):
return str == str[::-1]
Useful Function - Reversing A string
test_string="test string"
reverse_test_string=test_string[::-1]
print(reverse_test_string)
Output: "gnirts tset"
Useful Function - Convert two lists into a dictionary
def convert_to_dictionary(keys, values):
return dict(zip(keys, values))
keys = [1, 2, 3]
values = ['X', 'Y', 'Z']
print(convert_to_dictionary(keys, values)) # {1: 'X', 2: 'Y', 3: 'Z'}
Iteration
For Loop
The following example uses a for loop to find the number of occurrences of a specified sub_string. In below example, the number returned would be 2.
def count_substring(string, sub_string):
count = 0
for i in range(len(string)):
if string[i:].startswith(sub_string):
count += 1
return count
count_substring('hello', 'l')
While Loop
The following example uses a while loop to find the factorial on an integer n.
def factorial(n):
result = 1
while(n >= 1):
result = result * n
n = n - 1
return result
factorial(5)
Printing ASCII value of character
Python program to print ASCII Value of Character
c = '*'
print("The ASCII value of '" + c + "' is", ord(c))
OUTPUT:The ASCII value of g is 42
Quick Math
This script is used to add (or multiply or divide or subtract) multiple numbers in a single command line.
import math
import sys
if len(sys.argv) < 4:
print("Usage: quickmath.py <add|mul|div|sub|avg> <num01> <num02> [num03..num99]")
exit(1)
w_addition = {"+", "add", "addition", "plus"}
w_subtraction = {"-", "sub", "subtraction", "minus"}
w_multiply = {"*", "x", "mul", "multiply"}
w_divide = {"/", "div", "divide"}
for counter in range(2, len(sys.argv)):
if not sys.argv[counter].isdigit():
print("Usage: quickmath.py <add|mul|div|sub|avg> <num01> <num02> [num03..num99]")
exit(1)
result = float(sys.argv[2])
if sys.argv[1] in w_addition:
for counter in range(3, len(sys.argv)):
result = result + float(sys.argv[counter])
elif sys.argv[1] in w_subtraction:
for counter in range(3, len(sys.argv)):
result = result - float(sys.argv[counter])
elif sys.argv[1] in w_multiply:
for counter in range(3, len(sys.argv)):
result = result * float(sys.argv[counter])
elif sys.argv[1] in w_divide:
for counter in range(3, len(sys.argv)):
result = result / float(sys.argv[counter])
else:
print("Usage: quickmath.py <add|mul|div|sub|avg> <num01> <num02> [num03..num99]")
exit(1)
print(str(result))
Validate JSON
This script will read a file and either pass the file as being a valid JSON file, or die a horrible death.
#!/usr/bin/env python3
import os
import sys
import json
if len(sys.argv) > 1:
if os.path.exists(sys.argv[1]):
file = open(sys.argv[1], "r")
json.load(file)
file.close()
print("Validate JSON!")
else:
print(sys.argv[1] + " not found")
else:
print("Usage: checkjson.py <file>")
Generate Random Password
This script will generate random password with following rules:
- 6-20 characters
- at least one uppercase character
- at least one lowercase character
- at least one digit
- at least one special character (!, @, #, $, %, ^, &, *)
- no more than 2 characters repeating consecutively
import random
LOWERCASE_CHARS = tuple(map(chr, xrange(ord('a'), ord('z')+1)))
UPPERCASE_CHARS = tuple(map(chr, xrange(ord('A'), ord('Z')+1)))
DIGITS = tuple(map(str, range(0, 10)))
SPECIALS = ('!', '@', '#', '$', '%', '^', '&', '*')
SEQUENCE = (LOWERCASE_CHARS,
UPPERCASE_CHARS,
DIGITS,
SPECIALS,
)
def generate_random_password(total, sequences):
r = _generate_random_number_for_each_sequence(total, len(sequences))
password = []
for (population, k) in zip(sequences, r):
n = 0
while n < k:
position = random.randint(0, len(population)-1)
password += population[position]
n += 1
random.shuffle(password)
while _is_repeating(password):
random.shuffle(password)
return ''.join(password)
def _generate_random_number_for_each_sequence(total, sequence_number):
""" Generate random sequence with numbers (greater than 0).
The number of items equals to 'sequence_number' and
the total number of items equals to 'total'
"""
current_total = 0
r = []
for n in range(sequence_number-1, 0, -1):
current = random.randint(1, total - current_total - n)
current_total += current
r.append(current)
r.append(total - sum(r))
random.shuffle(r)
return r
def _is_repeating(password):
""" Check if there is any 2 characters repeating consecutively """
n = 1
while n < len(password):
if password[n] == password[n-1]:
return True
n += 1
return False
if __name__ == '__main__':
print generate_random_password(random.randint(6, 30), SEQUENCE)
Note :
As a python developer, be careful with Python indentation. sometimes even if lines look visually indented, from python perspective they maybe are not indented & causes errors. IDEs like PyCharm are useful for debugging and avoiding common errors such as this.