## Python Reference Sheet for Compsci 101, Exam 1

On this page we'll keep track of the Python types, functions, and operators that we've covered in class. You can also review the online Python References for more complete coverage, BUT NOTE there is far more detail on the Python documenation than we will cover!

The reference page below is all you should need to complete the exam.

Mathematical Operators
Symbol Meaning Example
+ addition 4 + 5 = 9
- subtraction 9 - 5 = 4
* multiplication 3*5 = 15
/ division 6/4 = 1.5
// floor division 6//4 = 1
% mod/remainder 5 % 3 = 2
** exponentiation 3**2 = 9, 2**3 = 8
String Operators
+ concatenation "ab"+"cd"="abcd"
* repeat "xo"*3 = "xoxoxo"
Comparison Operators
== is equal to 3 == 3 is True
!= is not equal to 3 != 3 is False
>= is greater than or equal to 4 >= 3 is True
<= is less than or equal to 4 <= 3 is False
> is strictly greater than 4 > 3 is True
< is strictly less than 3 < 3 is False
Boolean Operators
`x=5`
not flips/negates the value of a bool (not x == 5) is False
and returns True only if both parts of it are True (x > 3 and x < 7) is True
(x > 3 and x > 7) is False
or returns True if at least one part of it is True (x < 3 or x > 7) is False
(x < 3 or x < 7) is True
Type Conversion Functions
int(x) turn x into an integer value int("123") == 123
int can fail, e.g., int("abc") raises an error
float(x) turn x into an float value float("2.46") == 2.46
float can fail, e.g., float("abc") raises an error
str(x) turn x into a string value str(432) == "432"
type(x) the type of x type(1) == int
type(1.2) == float
String Functions
`s="colorful"`
Name Returns Example
.find(str) index of first occurrence s.find("o") == 1
s.find("e") == -1
.rfind(str) index of last occurrence s.rfind("o") == 3
s.rfind("e") == -1
.count(str) number of occurrences s.count("o") == 2
s.count("r") == 1
s.count("e") == 0
.strip() copy with leading/trailing whitespace removed "   big ".strip() == "big"
.split() list of "words" in s separated by whitespace "big bad dog".split() == ["big","bad", "dog"]
.split(",") list of "items " in s that are separated by a comma
In general can split on any string, not just a comma, e.g., s.split(":") will split on a colon and s.split("gat") will split on the string "gat".
"this,old,man".split(",") == ["this", "old", "man"]
' '.join(lst) concatenate elements of lst, a list of strings, separated by ' ' or any string ':'.join(['a','b','c']) == "a:b:c"
.startswith(str) boolean if starts with string s.startswith("color") == True
s.startswith("cool") == False
.endswith(str) boolean if ends with string s.endswith("ful") == True
s.endswith("color") == False
.upper() uppercase of s s.upper() == "COLORFUL"
.lower() lowercase of s "HELLO".lower() == "hello"
Miscellaneous Functions
len(x) length of sequence x, e.g., String/List len("duke") == 4
list(str) a list of the characters from string str list("cards") == ['c','a','r','d','s']
sorted(x) return list that is sorted version of sequence/iterable x, doesn't change x sorted("cat") == ['a','c','t']
range(x) a sequence of integers starting at 0 and going up to but not including x range(5) == [0, 1, 2, 3, 4]
range(start, stop) a sequence of integers starting at start and going up to but not including stop range(3, 7) == [3, 4, 5, 6]
range(start, stop, inc) a sequence of integers starting at start and going up to but not including stop with increment inc range(3, 9, 2) == [3, 5, 7]
min(x, y, z) minimum value of all arguments min(3, 1, 2) == 1
min("z", "b", "a") == "a"
max(x, y, z) maximum value of all arguments max(3, 1, 2) == 3
max("z", "b", "a") == "z"
abs(x) absolute value of the int or float x abs(-33) == 33
abs(-33.5) == 33.5
List Functions
sum(lst) returns sum of elements in list lst sum([1,2,4]) == 7
max(lst) returns maximal element in lst max([5,3,1,7,2]) == 7
lst.append(...) append an element to lst, changing lst [1,2,3].append(8) == [1,2,3,8]
lst.count(elt) return number of occurrences of elt in `lst` [1,2,1,2,3].count(1) == 2
Math Functions (import math)
math.pi 3.1415926535897931
math.sqrt(num) returns square root of num as float math.sqrt(9) == 3.0
File Functions
open("filename") opens a file, returns file object f = open("foo.txt")
f.readlines() returns the entire file as a list of lines (strings) s = f.readlines()
f.close() close the file f
Random Functions (import random)
random.randint(start, end) Returns a random integer between start and end. Unlike range() and list slicing, the largest value it can return is end, not end-1.
random.random() Returns a random float between 0 and 1.