A short summary of the functions, operators, and commands we discuss in class.
| Command | Description | Example |
pwd | Prints the current directory. | pwd |
ls | Lists the contents of the current directory. | ls |
cd | Changes the current directory. Can be called with the name of a subdirectory of the current folder or .. to go one folder up. (You can also use absolute paths or longer relative path.) | cd .. (goes one folder up)
cd test (goes into the folder test that is located in the current directory) |
cat | Prints the contents of a file. Should be called with the name of the file to print. | cat test.py |
mkdir | Creates a new directory. Takes the name of the new folder as an argument. | mkdir myNewFolder |
python | If called without a parameter, the python shell is started. If called with a file name of a python script, the script is executed. | python (Starts the python shell.)
python myScript.py (Executes the script myScript.py.) |
| Operator | Description | Example |
+ | Adding two numbers, or concatenating two strings. | 4 + 5
"Hello " + "World!" |
- | Subtracting two numbers. | 6 - 5 |
* | Multiplying two numbers or 'multiplying' a string. | 6 * 5
"Hello" * 4 |
/ | Dividing two numbers. | 6 / 3 |
% | Calculates modulo of two numbers. Divides left number by right number and returns remainder | 6 % 3 (Returns 0, as 3 * 2 + 0 = 6)
8 % 3 (Returns 2, as 3 * 2 + 2 = 8) |
== | Compares two values and returns True if the values are equal, otherwise False. | "Hello" == "World" (Returns False)
5 == 5 (Returns True) |
!= | Compares two values and returns True if the values are not equal, otherwise False. | "Hello" != "World" (Returns True)
5 != 5 (Returns False) |
> | Compares two values and returns True if the the first value is greater than the second, otherwise False. | 9 > 8 |
< | Compares two values and returns True if the the first value is smaller than the second, otherwise False. | 5 < 8 |
>= | Compares two values and returns True if the the first value is greater or equal than the second, otherwise False. | 8 >= 8 (Returns True) |
<= | Compares two values and returns True if the the first value is smaller or equal to the second, otherwise False. | 5 <= 8 (Returns True) |
= | Assigning a value to a variable. | a = 4 (The variable a will now have the value 4.) |
| Function | Description | Example |
print() | Writing something to the python shell or terminal. | print("Hello World!") |
type() | Returns the type of a value or variable. | type("Hello World!")
type(5)
type(a) (Where a could be 1.34) |
input() | Prints the text that is given to the function, waits for the user to enter some text and hit enter, then returns the input of the user. | input("What's your name? ") |
float() | Tries to turn whatever argument is given to the function into a float value. | float("4.5") |
int() | Tries to turn whatever argument is given to the function into an integer value. | int("4.5") |
str() | Tries to turn whatever argument is given to the function into a string value. | str(4.5) |
randint() | Lets you generate a randome number in a range you provide. | from random import randint
randint(1, 5) |
| Keyword/Statement | Description | Example |
# | Use this character if you want to make a comment on a piece of code. Python will ignore whatever you write after the # character and continue with the next line. | # define variable
a = 5
# now add one
a = a + 1 |
if condition:
if block
elif condition:
elif block
else:
else block | Allows you to execute different code depending on a condition. | if a < 5:
print("a is smaller than 5")
elif a > 5:
print("a is greater than 5")
else:
print("a equals 5") |
while condition:
while block | Lets you repeat the execution of a specific code block until a the specified condition is no longer true. | x = 1
while x < 5:
print("x is " + x)
x = x + 1 |
for element in elements:
for block | Lets you repeat the execution of a specific code block for each element in a list. | numbers = [1,3,5]
for num in numbers:
print("number is " + num) |
def | Use this keyword to define a function. | def myFunc():
print("Hello World!") |
return | Use this keyword to return something from a function. | def myFunc():
return 5 |
import | Allows you to use functions from a different Python file (module). | import myModule
# now you can call the function
myModule.myFunc() |
from module import part | Allows you to use specific functions from a different Python file (module). | from myModule import myFunc
# now you can call the function
myFunc() |
| Method | Description | Example |
append() | Is a method of lists. Appends the value you provide to the list it is called on. | my_list = [1, 2, 3]
my_list.append(4) (Afterwards the list looks like: [1, 2, 3, 4]) |
list[i] | Is a method of lists. Returns the ith element of the list list | my_list = [1, 2, 3]
my_list[2] (Returns 3. Remember that indices start at 0.) |
keys() | Is a method of dictionaries. Returns all keys of the dictionary. | my_dict = {'one':1, 'two':2}
my_dict.keys() (Returns: 'one, 'two') |
values() | Is a method of dictionaries. Returns all values of the dictionary. | my_dict = {'one':1, 'two':2}
my_dict.values() (Returns: 1, 2) |
items() | Is a method of dictionaries. Returns all tuples of the dictionary in a list. | my_dict = {'one':1, 'two':2}
my_dict.items() (Returns: [('two', 2), ('one', 1)]) |
get() | Is a method of dictionaries. Returns all the value for the provided key or None if the key doesn't exist. If a default value is provided, it returns that one instead of none. | my_dict = {'one':1, 'two':2}
my_dict.get('one') (Returns: 1)
my_dict.get('three', 5) (Returns 5) |