math operations Flashcards
sep=” “
space between two words
end=”\n”
end of line
int + string
string / integer
unsupported operand type– type error
string * 2
stringstring
\n
next line
"
to escape quotation mark
sentense.replace
will replace a word “ I “ or a character
f string
string format
(x / y)
exact division answer
x//y
only whole number
x%y
remainder
x += 3
x = x + 3
x -= 3
x = x - 3
x /= 3
x = x / 3
x %= 3
x = x % 3
x //= 3
x = x // 3
x **= 3
x = x ** 3
is
Returns True if both variables are the same object
x is y
in
Returns True if a sequence with the specified value is present in the object
x in y
thislist = [“apple”, “banana”, “cherry”, “orange”, “kiwi”, “melon”, “mango”]
print(thislist[:4])
This example returns the items from the beginning to, but NOT including, “kiwi”:
[‘apple’, ‘banana’, ‘cherry’, ‘orange’]
This example returns the items from “cherry” to the end:
thislist = [“apple”, “banana”, “cherry”, “orange”, “kiwi”, “melon”, “mango”]
print(thislist[2:])
This example returns the items from “cherry” to the end:
[‘cherry’, ‘orange’, ‘kiwi’, ‘melon’, ‘mango’]
thislist = [“apple”, “banana”, “cherry”, “orange”, “kiwi”, “melon”, “mango”]
print(thislist[-4:-1])
This example returns the items from “orange” (-4) to, but NOT including “mango” (-1):
[‘orange’, ‘kiwi’, ‘melon’]
thislist = [“apple”, “banana”, “cherry”]
thislist[1:3] = [“watermelon”]
print(thislist)
Change the second and third value by replacing it with one value:
[‘apple’, ‘watermelon’]
thislist = [“apple”, “banana”, “cherry”]
thislist[1:2] = [“blackcurrant”, “watermelon”]
print(thislist)
Change the second value by replacing it with two new values:
[‘apple’, ‘blackcurrant’, ‘watermelon’, ‘cherry’]
Insert “watermelon” as the third item:
thislist = [“apple”, “banana”, “cherry”]
thislist.insert(2, “watermelon”)
print(thislist)
[‘apple’, ‘banana’, ‘watermelon’, ‘cherry’]
To add an item to the end of the list, use the append() method:
Using the append() method to append an item:
thislist = [“apple”, “banana”, “cherry”]
thislist.append(“orange”)
print(thislist)
[‘apple’, ‘banana’, ‘cherry’, ‘orange’]
To insert a list item at a specified index, use the insert() method.
The insert() method inserts an item at the specified index:
Example
Insert an item as the second position:
thislist = [“apple”, “banana”, “cherry”]
thislist.insert(1, “orange”)
print(thislist)
[‘apple’, ‘orange’, ‘banana’, ‘cherry’]
The remove() method removes the specified item.
Example
Remove “banana”:
thislist = [“apple”, “banana”, “cherry”]
thislist.remove(“banana”)
print(thislist)
[‘apple’, ‘cherry’]
Addition + and subtraction - has the same precedence, and therefor we evaluate the expression from left to right:
print(5 + 4 - 7 + 3)
2
List Comprehension
List comprehension offers a shorter syntax when you want to create a new list based on the values of an existing list.
Example:
Based on a list of fruits, you want a new list, containing only the fruits with the letter “a” in the name.
Without list comprehension you will have to write a for statement with a conditional test inside:
Example
fruits = [“apple”, “banana”, “cherry”, “kiwi”, “mango”]
newlist = []
for x in fruits:
if “a” in x:
newlist.append(x)
print(newlist)
[‘apple’, ‘banana’, ‘mango’]
Condition
The condition is like a filter that only accepts the items that valuate to True.
Example
Only accept items that are not “apple”:
newlist = [x for x in fruits if x != “apple”]
The condition is like a filter that only accepts the items that valuate to True.
[‘banana’, ‘cherry’, ‘kiwi’, ‘mango’]
unary operation
only one value is involved
it can be unary + and Unary -
examples
x =5
y= -3
print(-1.0) # -1
print(-x) # -5
print(-y) # 3
string format()
The format() method allows you to format selected parts of a string.
Add a placeholder where you want to display the price:
price = 49
txt = “The price is {} dollars”
print(txt.format(price))
The price is 49 dollars
Format the price to be displayed as a number with two decimals:
txt = “The price is {:.2f} dollars”
The price is 49.00 dollars
Close the file when you are finish with it:
f = open(“demofile.txt”, “r”)
print(f.readline())
f.close()
Hello! Welcome to demofile.txt
To open a file for reading it is enough to specify the name of the file:
f = open(“demofile.txt”)
To open the file, use the built-in open() function.
The open() function returns a file object, which has a read() method for reading the content of the file:
f = open(“demofile.txt”, “r”)
print(f.read())
Hello! Welcome to demofile.txt
This file is for testing purposes.
Good Luck!
To write to an existing file, you must add a parameter to the open() function:
“a” - Append - will append to the end of the file
“w” - Write - will overwrite any existing content
f = open(“demofile2.txt”, “a”)
f.write(“Now the file has more content!”)
f.close()
Hello! Welcome to demofile2.txt
This file is for testing purposes.
Good Luck!Now the file has more content!
** Open command with ‘a’ attribute opens an existing file and appends to that file.
** w attribute creates a new file and writes to it
open and read the file after the overwriting:
Open the file “demofile3.txt” and overwrite the content:
f = open(“demofile3.txt”, “w”)
f.write(“Woops! I have deleted the content!”)
f.close()
f = open(“demofile3.txt”, “r”)
print(f.read())
Woops! I have deleted the content!
Create a New File
“x” - Create - will create a file, returns an error if the file exist
“a” - Append - will create a file if the specified file does not exist
“w” - Write - will create a file if the specified file does not exist
Example
Create a file called “myfile.txt”:
f = open(“myfile.txt”, “x”)
Result: a new empty file is created!
delete a file
import os
os.remove(“demofile.txt”)
Check if File exist:
Check if file exists, then delete it:
import os
if os.path.exists(“demofile.txt”):
os.remove(“demofile.txt”)
else:
print(“The file does not exist”)
Delete Folder
os.rmdir()
reverse a string
“Hello World”[::-1]
What function is used to convert a string to an integer?
Use int to convert strings to integers.
Math fabs
Return the absolute value of x.
math.fmod(x, y)
function fmod() is generally preferred when working with floats, while Python’s x % y is preferred when working with integers.
math.frexp(x)
m is a float and e is an integer such that x == m * 2**e exactly
math.isnan(x)
Return True if x is a NaN (not a number), and False otherwise.
math.isqrt(n)
Return the integer square root of the nonnegative integer n. This is the floor of the exact square root of n, or equivalently the greatest integer a such that a² ≤ n.
date.strftime(format)
Return a string representing the date, controlled by an explicit format string. Format codes referring to hours, minutes or seconds will see 0 values.
datetime.weekday()
Return the day of the week as an integer, where Monday is 0 and Sunday is 6. The same as self.date().weekday(). See also isoweekday().
random.randrange(start, stop[, step])
Return a randomly selected element from range(start, stop, step).
random.shuffle(x)
Shuffle the sequence x in place.
To shuffle an immutable sequence and return a new shuffled list, use sample(x, k=len(x)) instead.
random.choice(seq)¶
Return a random element from the non-empty sequence seq. If seq is empty, raises IndexError.
random.sample(population, k, *, counts=None)
Return a k length list of unique elements chosen from the population sequence. Used for random sampling without replacement.
