Basic ideas

elemets

Actually, elements is not a formal name, but I love to say so. That it solve from a really natural problem, how do we describe our world to the computer?

Exactly, we use words to describe our ideas, and we use numbers to count. So here are two sorts of elements, numbers and text.

num = 0
text = "hello"
text2 = 'hello'

As you can see here, that we can use both "" and ” to describe a text, but actually there ae something deeper in number and text. Notice that I use ”=” but it seems it is not the equal, actually, we use one = to describe “define” something, I define “hello” to the variable text, actually, it is another widely form of equal, but remember the order. We use == to show the truly equal.

number

Here are 2 types of numbers: int and float. Actually, you can see int and float as functions. As int, it turns a number to its integer part, While

class int(number=0, /)
class int(string, /, base=10)

So int([what you want to write here], [base of what you want to type and defaultly 10:2,8,16])

int(123.45) # 123
int('123') # 123
int('   -12_345\n')# -12345
int('FACE', 16) # F A C E from 16 to decimal, which is 64206
int('0xface', 0) # base 0 means let the computer to check the prefix: 0x: 16; 0b: 2; 0o: 8
int('01110011', base=2) # 115

About float

float('+1.23') # 1.23
float('   -12345\n') # -12345.0
float('1e-003') # 0.001, this means exponent by 10, like 1 * 10 ^(-3)
float('+1E6') # samely, 100000.0
float('-Infinity') # -inf, infinity is actually another form of float value.

sign:          "+" | "-"
infinity:      "Infinity" | "inf"
nan:           "nan"
digit:         <a Unicode decimal digit, i.e. characters in Unicode general category Nd>
digitpart:     digit (["_"] digit)*
number:        [digitpart] "." digitpart | digitpart ["."]
exponent:      ("e" | "E") [sign] digitpart
floatnumber:   number [exponent]
absfloatvalue: floatnumber | infinity | nan
floatvalue:    [sign] absfloatvalue

We can also do some basic computation here: +,-,*,/ are actually what you think, but there are still something out of range.

17/3 # 5.66666666667
17 // 3 # divide but only the int part, so it is 5
17 % 3 # remainder of the division 2
5 ** 2 # ** means power, so this is 5^2 =25

List

Actually, I’d like to say list is the most basic and important part of the whole python, whatever we want, a bench of things, are lists. We do orderings, we do executings, we do algorithms, they are all based on lists.

list = [1,2,3]

Actually, it is pretty easy to understand, use ”[]”, abnd comma for each element. And here are some basic properties in lists

list = [1,2,3] # We define a list here, "list" is somewhere a variable, if we want, we can change its value later
print(list[0]) # 1 exactly. 

Here is one thing pretty necessary to notice that list is counted from zero, where is out of our intuition. And what I use list[i] means the ith term in the list of “list”.