Types of Errors
IndexError |
Raised when the index of a sequence is out of range |
NameError |
Raised when a variable is not found in the local and global scope |
SyntaxError |
Raised by the parser when a syntax error is encountered |
TypeError |
Raised when a function/operation is applied to an object of an incorrect type |
UnboundLocalError |
Raised when a reference is made to a local variable in a function/method, but no value has been bound to that variable |
ZeroDivisionError |
Raised when the second operand of a division/module operation is zero |
ValueError |
Raised when a function gets an argument of a correct type but improper value |
MemoryError (RecursionError) |
Raised when an operation runs out of memory |
RuntimeError |
Raised when an error does not fall under any other category |
Alphabetical Order (ASCII Table, ord & chr)
48: 0 49: 1 50: 2 51: 3 52: 4 53: 5 54: 6 55: 7 56: 8 57: 9 58: : 59: ; 60: < 61: = 62: > 63: ? 64: @
65: A 66: B 67: C 68: D 69: E 70: F 71: G 72: H 73: I 74: J 75: K 76: L 77: M 78: N 79: O 80: P 81: Q 82: R 83: S 84: T 85: U 86: V 87: W 88: X 89: Y 90: Z
97: a 98: b 99: c 100: d 101: e 102: f 103: g 104: h 105:i 106: j 107: k 108: l 109: m 110: n 111: o 112: p 113: q 114: r 115: s 116: t 117: u 118: v 119: w 120: x 121: y 122:z
ord('A') = 65, chr(66) = 'B'
0 < 9 < 'A' < 'Z' < 'a' < 'z'
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z |
Loop Statements
break |
Terminates the whole loop |
continue |
Stops the current iteration of the loop, and goes on to the next iteration of the loop |
pass |
Does nothing and continues the rest of the code inside the current iteration of the loop |
Boolean Values
False evaluates to 0; int(False) == 0, while True evaluates to 1; int(True) = 1
On the other hand, any empty str, tuple, list ('', (), []), the value 0 and None evaluates to False; bool(0/None/""/()) = False, and any other expression will evaluate to True; bool(1/-95/"CS1010S is fun"/("C", "S", "S", "U", "C", "K", "S")) = True |
String Slicing Mechanism
s = 'abcdef '
0 1 2 3 4 5
-6-5-4-3-2-1
s[start(inclusive):stop(exclusive):step]
e.g.
s[1:] = 'bcdef'
s[3::-1] = 'dcba'
s[6:] = ''
s[2:-6:-1] = 'cb' |
Tuple and string functions
len() |
Returns the length of the string/number of items in the tuple |
max() |
Returns the largest item in the tuple |
min() |
Returns the smallest item in the tuple |
sum() |
Returns the sum of all elements in the tuple |
tuple() |
Converts an iterable into a tuple |
tuple.count(ele) |
Counts the number of occurrences of an element in a tuple |
str.index(ele) |
Searches the string for a specified ele from the left and returns the position of where it was found |
Checking data type
type(value) == Type |
isinstance(value, Type) |
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Orders of Growth (OOG)
O(1) < O(log n) < O(n) < O(n log n) < O(n2) < O(2n) < O(n!) < O(nn)
O(1): Indexing, replacing variable name
O(log n): Constantly halving/doubling a number (depending on direction)
O(n): Going through the whole tuple/string (for loop/recursion)
O(n2): Going through the whole tuple once for each element (Usually nested for loop)
O(2n): The tree splits into 2/x number of branches for each level (Usually for recursion tree)
Sample Answer:
Time: O(n), there is a total of n recursive calls.
Space: O(n), there is a total of n recursive calls, and each call will take up space on the stack.
Time: O(n), the loop will iterate n times.
Space: O(1), no extra memory is needed because the variables are overwritten with the new values. |
Big O Notation
Time Complexity: Sum of time taken at each level of the recursion tree (number of recursive calls, intensive operations) |
Time Complexity: Count the loops, and the intensive operations (eg string concatenation) |
Space Complexity: Height of the recursion tree (Also check for strings, tuples, etc) |
Space Complexity: Count the variables stored (need to store individual chars for strings) |
String Concatenation (2)
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