1 Something about `print`

syntax	explanation
`print(str1, str2, sep = "")`	print strings separately
`print(str1 + str2)`	print strings as one string
`print(f'{my_var}')`	f-string interpret what inside the {}
`print('%type' %my_var)`	`%d`: integer; `%f`: float; `%s`: string; `%b`: binary; (doc)
`print(\n)`	print use escape characters
`print(f'{my_var:n[type]}')`	print the variable at a certain length
`{:<}`, `{:>}`, `{:^}`	left aligned, right aligned, centred

syntax	explanation
`+`, `-`, `*`, `/`	addition, subtraction, multiplication, division
`**`	exponentiation
`//`	integer division
`%`	modulus; the remainder of a deviation

2 Import modules

import numpy as np
print(np.sin(np.pi))

3 Variables and objects

type() : check data types.

Numeric: int, float, complex;
Sequence: str, list, range, tuple
Boolean
Set
Dictionary
number objects and string objects

3.1 Strings

syntax	explanation
`my_str[i]`	returns the $i + 1$ ^th character in `string`
`my_str[-i]`	returns the $i$ ^th from the end
`len(my_str)`	the length of the string
`max(my_str)`, `min(my_str)`	alphabetically
`sorted(my_str)`	from smallest to largest
`my_str.capitalize()`	capitalize the first letter of the string
`my_str.split()`	split the string

3.2 Booleans

Operators:

syntax	explanation
`and`, `or`, `not`	logical operators
`==`, `<`, `<=`, `!=`	comparison operators

3.3 Numbers

Floating points numbers: 1.0e-6 is $\times 10^{-6}$ .

3.4 Type casting

int(), float(), str().

bool(0) and bool('') are false.

3.5 List

List can contain almost any other object.

my_list = ['my', 1, 4.5, ['you', 'they'], 432, -2.3, 33]
emplist = []
print(list_1 + list_2)
print('hellow'+'world')   # "helloworld"
my_list.append('extar')    # add an item to the end of a list
print(my_list[3][1])       # the outcome is "they"
print(sorted(numberlist)) # sort a list
print(12 * my_list)        # create a list with 12 repetition of my_list
print('you' in my_list[3]) # check if something is in a list

Useful tools:

syntax	explanation
`len(my_list)`	the length of the list
`my_list.append('a new element')`	add a new element to the list

Slicing:

a = [2, 5, 4, 8, 8]
print(a[1:3]) # the 2nd and 3rd | [5, 4]
print(a[2:])  # the 3rd to the last | [4, 8, 8]
print(a[:-2]) # the 1st to the 3rd from the last | [2, 5, 4]

syntax	explanation
`my_list[start:stop]`	from start to stop-1 共stop-start个
`my_list[start:]`	from start to len(l)-1
`my_list[:stop]`	from 0 to stop-1
`my_list[start:stop:step]`	from start to stop-1, with increment step
`my_list[::step]`	from 0 to len(l)-1, with increment step
`my_list[::]`, `my_list[:]`	all the elements

If j $=$ i, then a[i:j] and a[i:j:k] are empty lists, for any value of k.
If j $<$ i, then a[i:j] and a[i:j:k] are empty lists, for positive values of k.

4 `if` statements

if my_condition:
    [some instructions]

my_condition is a Boolean object.

if cond_1:
    [some instructions]
elif cond_2:
    [other instructions]
else:
    [other instructions]

5 Loops

5.1 `for` loops

for i in my_seq:
	[some instructions]

ranges: a sequence type

syntax	explanation
`range(j)`	$0$ , $1$ , $2$ , …, $j ? 1$ ; 共 $j$ 个.
`range(i, j)`	$i$ , $i + 1$ , $i + 2$ , …, $j ? 1$ ; 共 $j ? i$ 个.
`range(i, j, k)`	$i$ , $i + k$ , $i + 2 k$ , …, $i + m$ ; $\leq j-1$ .

5.2 `while` loops

while my_condition:
    [some instructions]

Use break to exit the loop conditionally:

while my_condition:
    [some instructions]
    if my_condition:
        break

6 Defining function

def my_func(inputs):
    [function body]
    return outputs

Outputs can be variables separated by commas.

7 Debugging and troubleshooting

Built-in exception types：

IndexError: a sequence subscript is out of range. r instance, here, we’re trying to access my_list[4], but my_list only has elements up to my_list[3].
NameError: the variable referred to does not exist – there is no box in memory with this label. This often comes up when you mistype a variable name.
SyntaxError: the code is not syntactically correct – it is not valid Python, so Python doesn’t know how to interpret it.
TypeError: a very common error to see when learning Python! This means that an operation or a function is applied to an object of the wrong type
ValueError: raised when an operation or function is applied to an object with the right type, but an invalid value. For example, the int() function can cast a string to an integer, if the string can be interpreted as a number.