Merge pull request #2 from AimenYaseen/python-concepts

Python concepts

Author: AimenYaseen

python_for_coding_interviews/1_variables.py

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+"""
+In python , variables are dynamically typed.
+It means their data type is determined at runtime.
+No need to specify their datatype like we do in c++ e.g. int x;
+"""
+
+n = 0
+print('n =', n)
+# n = 0
+
+n = "abc"
+print('n =', n)
+# n = abc
+
+# Multiple assignments
+n, m = 0, "abc"
+n, m, z = 0.125, "abc", False
+
+# Increment
+n = n + 1  # good
+n += 1  # good
+# n++       # bad; there is no such operator in python
+
+# None is null (absence of value)
+n = 4
+n = None
+print("n =", n)
+# n = None

python_for_coding_interviews/2_if_statements.py

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+"""
+In python, there is no parenthesis and curly brackets.
+We use indentation to specify a piece of block instead of brackets or parenthesis.
+So, If statements also don't need that
+"""
+
+n = 1
+if n > 2:
+    n -= 1
+elif n == 2:
+    n *= 2
+else:
+    n += 2
+
+"""
+But Parentheses needed for multi-line conditions.
+Logical Operators
+1. and = &&
+2. or  = ||
+"""
+n, m = 1, 2
+if ((n > 2 and
+     n != m) or n == m):
+    n += 1

python_for_coding_interviews/3_loops.py

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+"""
+Python have two loops, while and for loop.
+
+While loop is used when you don't know about the number of iterations.
+Example, you have to take input from user repeatedly until it enters correct input.
+
+For loop is used when you know about the number of iterations.
+Example, print a number 10 times.
+
+"""
+
+n = 5
+while n < 5:
+    print(n)
+    n += 1
+
+"""
+We use range function for iteration in for loop.
+Some facts about range function:
+1. By default, it starts with 0.
+2. range(stop_value) equals to i < stop_value. It means last digit is always exclusive.
+3. You can also specify the starting value like this => range(start, stop).
+4. By default, it increments by +1.
+5. You can also specify the incrementing value like this => range(start, stop, increment).
+"""
+
+# Looping from i = 0 to i = 4
+for i in range(5):
+    print(i)
+
+# Looping from i = 2 to i = 5
+for i in range(2, 6):
+    print(i)
+
+# Looping from i = 5 to i = 2 with -1 increment
+for i in range(5, 1, -1):
+    print(i)

python_for_coding_interviews/4_math.py

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+import math
+
+# Division is decimal by default
+print('5 / 2 = ', 5 / 2)
+# output => 2.5
+
+# Double slash rounds down to integer
+print('5 // 2 = ', 5 // 2)
+# output => 2
+
+# CAREFUL: most languages round towards 0 by default
+# python rounds towards minimum value
+# So negative numbers will round down
+print('-3 // 2 = ', -3 // 2)
+# output => -2 but it should be -1
+
+# A workaround for rounding towards zero
+# is to use decimal division and then convert to int.
+print('-3 // 2 = ', int(-3 / 2))
+# output => -1
+
+# Modding is similar to most languages
+print('10 % 3 = ', 10 % 3)
+# output => 1
+
+# Except for negative values
+print('-10 % 3 = ', -10 % 3)
+
+# To be consistent with other languages modulo use math fmod
+
+print(math.fmod(-10, 3))
+
+# More math helpers
+print(math.floor(3 / 2))  # rounds down
+print(math.ceil(3 / 2))  # rounds up
+print(math.sqrt(2))
+print(math.pow(2, 3))
+
+# Max / Min Int
+float("inf")
+float("-inf")
+
+# Python numbers are infinite so they never overflow
+print(math.pow(2, 200))
+
+# But still less than infinity
+print(math.pow(2, 200) < float("inf"))
+# output => True