READING FILES
f = open("my_file.txt","r")
file_as_string = f.read()
- Open the file my_file.txt and assign its
contents to s
import csv
f = open("my_dataset.csv","r")
csvreader = csv.reader(f)
csv_as_list = list(csvreader)
- Open the CSV file my_dataset.csv and assign its
data to the list of lists csv_as_list
STRINGS
s = "hello" - Assign the string "hello" to the
variable s
s = """She said,
"there's a good idea."
"""
- Assign a multi-line string to the variable s. Also
used to create strings that contain both " and '
characters
len(s) - Return the number of characters in s
s.startswith("hel") - Test whether s starts with
the substring "hel"
s.endswith("lo") - Test whether s ends with the
substring "lo"
"{} plus {} is {}".format(3,1,4) - Return the
string with the values 3, 1, and 4 inserted
s.replace("e","z") - Return a new string based
on s with all occurances of "e" replaced with "z"
s.split(" ") - Split the string s into a list of
strings, separating on the character " " and
return that list
NUMERIC TYPES AND
MATHEMATICAL OPERATIONS
i = int("5") - Convert the string "5" to the
integer 5 and assign the result to i
f = float("2.5") - Convert the string "2.5" to
the float value 2.5 and assign the result to f
5 + 5 - Addition
5 - 5 - Subtraction
10 / 2 - Division
5 * 2 - Multiplication
3 ** 2 - Raise 3 to the power of 2 (or 32)
27 ** (1/3) - The 3rd root of 27 (or 3√27)
x += 1 - Assign the value of x + 1 to x
x -= 1 - Assign the value of x - 1 to x
LISTS
l = [100,21,88,3] - Assign a list containing the
integers 100, 21, 88, and 3 to the variable l
l = list() - Create an empty list and assign the
result to l
l[0] - Return the first value in the list l
l[-1] - Return the last value in the list l
l[1:3] - Return a slice (list) containing the second
and third values of l
len(l) - Return the number of elements in l
sum(l) - Return the sum of the values of l
min(l) - Return the minimum value from l
max(l) - Return the maximum value from l
l.append(16) - Append the value 16 to the end of l
l.sort() - Sort the items in l in ascending order
" ".join(["A","B","C","D"]) - Converts the list
["A", "B", "C", "D"] into the string "A B C D"
DICTIONARIES
d = {"CA":"Canada","GB":"Great Britain",
"IN":"India"} - Create a dictionary with keys of
"CA", "GB", and "IN" and corresponding values
of of "Canada", "Great Britain", and "India"
d["GB"] - Return the value from the dictionary d
that has the key "GB"
d.get("AU","Sorry") - Return the value from the
dictionary d that has the key "AU", or the string
"Sorry" if the key "AU" is not found in d
d.keys() - Return a list of the keys from d
d.values() - Return a list of the values from d
d.items() - Return a list of (key, value) pairs
from d
MODULES AND FUNCTIONS
The body of a function is defined through
indentation.
import random - Import the module random
from math import sqrt - Import the function
sqrt from the module math
def calculate(addition_one,addition_two,
exponent=1,factor=1):
result = (value_one + value_two) ** exponent * factor
return result
- Define a new function calculate with two
required and two optional named arguments
which calculates and returns a result.
addition(3,5,factor=10) - Run the addition
function with the values 3 and 5 and the named
argument 10
BOOLEAN COMPARISONS
x == 5 - Test whether x is equal to 5
x != 5 - Test whether x is not equal to 5
x > 5 - Test whether x is greater than 5
x < 5 - Test whether x is less than 5
x >= 5 - Test whether x is greater than or equal to 5
x <= 5 - Test whether x is less than or equal to 5
x == 5 or name == "alfred" - Test whether x is
equal to 5 or name is equal to "alfred"
x == 5 and name == "alfred" - Test whether x is
equal to 5 and name is equal to "alfred"
5 in l - Checks whether the value 5 exists in the list l
"GB" in d - Checks whether the value "GB" exists in
the keys for d
IF STATEMENTS AND LOOPS
The body of if statements and loops are defined
through indentation.
if x > 5:
print("{} is greater than five".format(x))
elif x < 0:
print("{} is negative".format(x))
else:
print("{} is between zero and five".format(x))
- Test the value of the variable x and run the code
body based on the value
for value in l:
print(value)
- Iterate over each value in l, running the code in
the body of the loop with each iteration
while x < 10:
x += 1
- Run the code in the body of the loop until the
value of x is no longer less than 10
Data Science Cheat Sheet
Python Basics
LEARN DATA SCIENCE ONLINE
Start Learning For Free - www.dataquest.io
LEARN DATA SCIENCE ONLINE
Start Learning For Free - www.dataquest.io
BASICS, PRINTING AND GETTING HELP
type(x) - Return the type of the variable x (in this case, int for integer)
help(x) - Show documentation for the str data type
help(print) - Show documentation for the print() function
x = 3 - Assign 3 to the variable x
print(x) - Print the value of x
