Python notes

PYTHON

WEEK 1

Variables
- String: text, images, messages
- Integer: number without decimals
- Float: number with decimals
- print(type(variable)) in order to determine the type of the variable.

Variable type conversion
- Cannot add two different types of variables (e.g. one cannot add string and integer/float), so therefore conversion is necessary.
- Convert to:
o String (str(variable))
o Integer (int(variable))
o Float (float(variable))

Rules
- Separate by a comma (,)

Inputs
- input: requires user to fill data
- Asking the user to type a value, reading from a file, reading a network connection, accessing a database.
- Store the result in a variable. The variable type will be a string. One may need to convert the variable into an integer or a float.

Operations
- Standard operators in order of priority:
o Power (**)
o Multiply (*)
o Divide (/)
o Plus (+)
o Minus (–)
- Parentheses are used to show priority.

Output
- What is presented to the user.
- print: displays text.
- Integers and floats do not use quotation marks, whereas strings do.

Rounding numbers
- round (variable, decimal spaces)

WEEK 2

Conditions
- Doing different things depending on different values.
- If… then…, else….
- if condition:
print
- else:
print
print(“Ending statement”)
- Indentations: the spaces before print are mandatory.
- A condition is a calculation that has a Boolean result: it is either true or false.
o print(comparison)
o It will print either “true” or “false”
- Comparisons:
o < less than
o <= less than or equal
o > higher than
o >= higher than or equal
o == equal
o != not equal, indifferent

Multiple conditions
- When a and b are conditions:
o a and b: TRUE when both conditions are TRUE
o a or b: TRUE when any condition is TRUE.

, Control flow
- What instructions will be executed?
o Instructions run in sequence, line by line.
o In case of error, the code after the error is not executed,
o The code can be divided in blocks of code, blocks are indicated by the indentation.
 Lines at the same indentation level belong to the same block.
 Indentations should only happen when there is a need for a separate block: after if, for, while, defining a function, or a class. It
should not happen in the middle of a block, or it generates and issue.

Lists
- A list is a variable that contains not just one value, but multiple values.
- Values are called elements.
- Each element is stored at an index.
- Indexes start at 0.
- The number of elements is called length of the list.
- Create lists using [ ].
- Separate elements with (,).
- Do not call a variable “list”. It is a function name.
- Counting the number of elements in a list:
o len(the_list)
- Access:
o The first item has an index of 0.
o For convenience, the last item has an index of -1.
o If there are 5 items, the index goes from 0-4.
o Accessing element at index i (the_list [i]).
- Modification:
o Modification of the value of the element at index i.
o the_list[i] = new_value
- Concatenation:
o Putting two lists together.
o the_list1 + the_list2
o One can also add a list that contains only one string.
- Check if a value is in a list:
o The result is true or false.
o if value (not) in the_list:
print
Strings
- A list of characters, except no modification is possible.

For loops
- Print each letter in variable
for x in variable:
print (x)
- Print each item of list
for x in list:
print (x)
- Print a word multiple time
for x in list:
print (“Word”)
- Sum:
o Start with a total at 0.
o For each value in the list, add it to the total.
o for value in the_list.
o Example:
my_list = [1, 2, 3]
total = 0
for elt in my_list:
total = total + elt
print(total) if you want the total at the end of each element in the list
print(total) if you want the total at the end

Range
- Print numbers in a particular range
- for x in range(number):
print