PythonNotes

Šeit pierakstu lietas, ko iemācos pa ceļam, apgūstot Python ar Gūgles palīdzību - kad kaut ko vajag izdarīt, meklēju vajadzīgās funkcijas/paņēmienus.

2009-06-19

Hello world

print "Hello, world";

Main function

if __name__ == '__main__':
    print "Hello world";

Script execution

python yourscript.py

Get local timestamp

import time
print time.time()

Type casting

Type casting functions: int(), str(), list(), tuple(), dict().

a = 1.5
print int(a)
print str(a)
print int('0x1a', 16) // prints 26

Print with several arguments

Type all arguments to strings, concatenate them:

a = 5
print "this is an int: " + str(a)

Convert decimal to hexadecimal

print hex(67)

Get ASCII code of a character

print ord('A')

Reading/writing files

f = open("myfile.txt", "r")
contents = f.read()  // read the whole file
bytes5 = f.read(5) // read 5 bytes
outfile = open("output.txt", "w");
outfile.write("abc def");
f.close()
outfile.close()

Store/load variable to/from file

import pickle

t = [1, 3, 5]
f = open("myfile.txt", "w")
pickle.dump(f, t)
// ...

t = pickle.load(f)

Replace substring

s = "Hello, world!"
print s.replace("world", "python");

Split string by delimiter

a = "1;2;3"
print a.split(";")

2009-06-28

Base64 encode/decode

import base64
encoded = base64.b64encode('data to be encoded')
data = base64.b64decode(encoded)

2009-07-04

Defining array

arr = [1, 2, 3, 4, 5]

2009-07-08

Check if file exists

import os
os.path.exists("/path/to/file")

Create directories, including parent directories

import os
dir = "/path/to/dir"
if os.path.exists(dir) == False:
    os.makedirs(dir)

Note: os.makedirs issues error when trying to create directory which already exists.

Check if path entry is a directory

import os
os.path.isdir("/path/to/dir/or/file")

Looping over numbers

# loop 1..10:
for i in range(10):
    print i

# loop 3..20:
for i in range(3, 20):
    print i

Extracting a substring

s = "This is a string"
this = s[0:4]
isa = s[5:7]