- 1 Something about `print`
- 2 import modules
- 3 Variables and objects
- 3.1 Strings
- 3.2 Booleans
- 3.3 Numbers
- 3.4 Type casting
- 3.5 List
- 4 `if` statements
- 5 Loops
- 5.1 `for` loops
- 5.2 `while` loops
- 6 Defining function
- 7 Debugging and troubleshooting
| 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 |
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
| syntax | explanation |
|---|---|
| my_str[i] | returns the i + 1 i+1 i+1th character in string |
| my_str[-i] | returns the i i ith 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 |
Operators:
| syntax | explanation |
|---|---|
| and, or, not | logical operators |
| ==, <, <=, != | comparison operators |
Floating points numbers: 1.0e-6 is 1 × 1 0 − 6 1 times 10^{-6} 1×10−6.
3.4 Type castingint(), float(), str().
bool(0) and bool('') are false.
3.5 ListList 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.
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 0 0, 1 1 1, 2 2 2, …, j − 1 j-1 j−1; 共 j j j个. |
| range(i, j) | i i i, i + 1 i+1 i+1, i + 2 i+2 i+2, …, j − 1 j-1 j−1; 共 j − i j-i j−i个. |
| range(i, j, k) | i i i, i + k i+k i+k, i + 2 k i+2k i+2k, …, i + m i+m i+m; i + m ≤ j − 1 i+m leq j-1 i+m≤j−1. |
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 troubleshootingBuilt-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.
