In [1]:

from env_helper import info; info()



Page update time： 2024-09-25 16:23:27
Operating environment：
    Linux Distribution : Debian GNU/Linux 12 (bookworm)
    Operating System Kernel: Linux-6.1.0-25-amd64-x86_64-with-glibc2.36
    Python version: 3.11.2

Python Runtime Mode¶

Python interactive running mode¶

To get started quickly, let's first take a look at the usage of interactive running:

Under Linux, open the terminal and type python3 (if installing iPython, you can type ipython3 ). This opens up interactive Python Shell。

Content typed in the Shell

In [2]:

print('Hello, Python World!')



Hello, Python World!

print() format output function, output the parameters in parentheses, which can be strings or numbers. If the parameter is empty, the output result is also empty.

In [3]:

strval1 = 'Welcome '
strval2 = 'Python World!'     
strval1 + strval2

Out[3]:

'Welcome Python World!'

Assign values to variables strval1 and strcal2 . Format output variables.

Python runs program files¶

Another way is to write Python code to a file (instead of pasting line by line). In Linux, it can be done through a terminal, text editor (VIM with runtime environment configured), or IDE (such as Run it in PyCharm; Under Windows, it can be opened and run in a terminal or IDLE. This type of file is called a script file. Through this method, it is possible to modify and experiment with these settings, and then rerun the script.

Create a new file using a text editor and enter the following code:

In [4]:

print('Hello, Python World!')
strval1 = 'Welcome'
strval2 = 'Python World!'
print(strval1)
print(strval1 + strval2)



Hello, Python World!
Welcome
WelcomePython World!

Save the file with the suffix py . For example, save as demo1.py . Then open a DOS window on Windows and enter:

python3 path_to_filedemo1.py

Similar in Linux. If prompted that there is no Python program, refer to the previous section on environment variable settings.

Operating mode under Linux¶

In Linux, create a blank plain text file and add executable permissions to it:

chmod +x world.py

Then, add the following line of code at the beginning of the script file:

1

#!/usr/bin/env python3

Just like in interactive mode below, write the code to a file. Of course, the code should pay attention to its syntax. Finally, save the file. When saving, some editors or operating systems need to pay attention to the encoding of the text file. To use Python 3, you need to save the file as a UTF-8 encoded file.

Regarding the handling of Chinese, it is also a common issue in Python. Although Python 3 has greatly simplified the problem of file encoding, there are still many libraries that continue to use Python 2 in GIS applications. The explanation of this issue is sufficient to use a separate chapter, but it is not suitable to elaborate on it in this book, so there will not be too much explanation in this book.

In [41]:

path = r'e:\book'
print(path)



e:\book

In [42]:

print('** \n\t"\r **')



** 
 **

Escape character

In [43]:

len(path)

Out[43]:

7

length

In [44]:

str_val = 's ' + 'pam'
print(str_val)
str_val = 's '  'pam'
print(str_val)



s pam
s pam

It is recommended to use the former for readability when connecting 's ' + 'pam' or 's''pam'

In [45]:

print('=' * 10)



==========

Repeated output

In [46]:

print('abc'+str(9))



abc9

Python does not allow other types to appear in+expressions, manual conversion is required:

In [47]:

val = int('42')
print(val)
val  =str(42)
print(val)
val = float('42.0')
print(val)



42
42
42.0

String conversion

In [48]:

print(ord('s')) #Convert ASCII
print(type(ord('s'))) #Convert ASCII
print(chr(115)) #Convert characters
print(type(chr(115)))



115
<class 'int'>
s
<class 'str'>

Convert ASCII to characters

In [49]:

s='spam'
k = '|'.join(s)
print(k)
s='spam'
l  = list(s)
print(l)
k = '|'.join(l)
print(k)



s|p|a|m
['s', 'p', 'a', 'm']
s|p|a|m

Merge and Split

In [50]:

s =  s+'a'
s = s[3:] + 'b'
s = s.replace('pl','pa')

The string cannot be modified, but it can be modified by reassigning it

In [51]:

s = 'abcdefg'
print(s[1:])
print(s[1:-1])



bcdefg
bcdef

The indexing and slicing of strings, as mentioned earlier

In [52]:

str_val = 'abcd'
str_val = str_val.capitalize()
print(str_val)



Abcd

The first character of the string is capitalized

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str_val = str_val.lower()
print(str_val)



abcd

Convert all to lowercase

In [54]:

print(str_val.isalpha())
print(str_val.isdigit())



True
False

The isxxx function. For more information, please refer to the reference manual

In [55]:

str_val = '  abcdfgxabcdyzcdba '
str_val = str_val.strip()
print(str_val)
str_val = str_val.strip('a')
print(str_val)



abcdfgxabcdyzcdba
bcdfgxabcdyzcdb

Remove characters

In [56]:

tepstr = str_val
str_val = str_val.strip('bc')
print(str_val)
str_val = tepstr.strip('cb')
print(str_val)



dfgxabcdyzcd
dfgxabcdyzcd

In [57]:

str_val = list(str_val)
str_val.sort()
str_val = ''.join(str_val)
print(str_val)



abccdddfgxyz

String sorting

In [58]:

str_val = str_val.upper()
print(str_val)



ABCCDDDFGXYZ

All capitalized

In [59]:

ind_list = range(5, 15)
ind_list = [str(x) for x in ind_list]
print(ind_list)
str_list = [ind.zfill(3) for ind in ind_list]
print(str_list)
''' Format output ：
%c Single character
%d Decimal integer
%o Octal integer
%s Character string
%x Hexadecimal integer,
lowercase letters
%X Hexadecimal integer,
 The letters are capitalized
    '''
str_val = 'The are %d %s in the team.' % (2, 'girls')
print(str_val)



['5', '6', '7', '8', '9', '10', '11', '12', '13', '14']
['005', '006', '007', '008', '009', '010', '011', '012', '013', '014']
The are 2 girls in the team.

Return a string of length and width, with the original string aligned to the right and padded with 0 in front