Python

#!/usr/bin/python
 
s = 'Hello World!';
 
#access element
print(s[0]); #H
 
#slicing
print(s[:2]); #He

#slice
sl = slice(0, 10, 2);
print(s[sl]); #HloWr
 
#concatenation
print(s+' ...');
 
#repeat
print(s*2);
 
#in
if 'H' in s:
    print('Contain H');
 
#raw string, suppresses actual meaning of escape characters
print(r'raw string\n');
s = 'raw string\n';
print('%r' % s) # output string as raw string

#!/usr/bin/python
 
s = 'Hello World!';
 
#capitalize, capitalizes first letter of string
print(s.capitalize());
 
#center
print(s.center(20, '*'));
 
#count
print(s.count('l'));
 
#endswith
if s.endswith('!'):
    print('end with ! ...');
 
#find
print(s.find('or')); #7

#index, find a string and raise an exception if the string is not found
print(s.index('or'));

#join
c = '-';
print(c.join(['a', 'b', 'c']));

#lower
print(s.lower());

#replace
print(s.replace('l', '-', 2));

#split
str = "Line1-abcdef, \nLine2-abc, \nLine4-abcd";
print(str.split());
import re
print(re.split('\n|, ',str)) # use multiple delimiter

#strip
print('  Hello ... '.strip());

#upper
print(s.upper()); #HELLO WORLD!

Pattern

^, beginning of a line
$, end of a line
., matches any single character except newline
[...], matches any single character in brackets
[^...], matches any single character not in brackets
*, matches 0 or more occurrences of preceding expression
+, matches 1 or more occurrence of preceding expression
?, matches 0 or 1 occurrence of preceding expression
re{n}, match exact n time
re{n, m}, matches at least n and at most m occurrences
a|b, matches either a or b
\w, match word characters
\W, match none word characters
<.*>, greedy repetition
<.*?>, none greedy repetition, matches the smallest number of repetitions

Flags

re.I, performs case-insensitive matching
re.M, makes $ match the end of a line (not just the end of the string) and makes ^ match the start of any line

#!/usr/bin/python
 
import re;
 
phone = "2004-959-559 # This is Phone Number"
 
#match
m = re.match(r'(\d+)-(\d+)-\d+.*', phone);
if m:
    print(type(m));
    print(m.group()); #2004-959-559 # This is Phone Number
    print(m.group(1)); # 2004
    print(m.groups()); # ('2004', '959')
 
#search
s = re.search(r'\d+', phone);
if s:
    print(type(s));
    print(s.group()); #2004
 
#findall
a = re.findall(r'\d+', phone);
print(a); #['2004', '959', '559']
 
#replace
r = re.sub(r'\d', '*', phone);
print(r); # ****-***-***, This is Phone Number

a sequence of code points, immutable

Python keep characters as unicode in memory

type 'str' represents unicode in Python 3, type 'bytes' represent byte string

#!/usr/bin/python

# unicode to str
s = 'Café';
print(type(s), len(s)); #'unicode', 4
s = u'Café';
print(type(s), len(s)); #'unicode', 4
print(type(s.encode('utf-8'))); #'bytes'

# read string from a file and print it to screen
f = open('temp.txt', 'rb');
l = next(f); #read a line and save it to byte string
print(type(l)) # byte string
l = l.decode('utf-8'); #decode str to unicode
print(type(l)); # 'unicode'
print(l); #陈, print encode unicode to str with utf-8
f.close();

# get unicode code point
c = ord(u'陈'); #38472
print(chr(38472)); #陈, do not print code point, it is encoded to str

read unicode, output unicode

#!/usr/bin/python

# read string from a file and print it to screen
f = open('temp.txt', 'r');

l = next(f); # 陈, read a line and save it to byte string
print(type(l)) # unicode

o = open('output.txt', 'w')
o.write(l) # convert byte string to unicode

o.close()
f.close();

read byte string, output unicode

#!/usr/bin/python

# read string from a file and print it to screen
f = open('temp.txt', 'rb');

l = next(f); # 陈, read a line and save it to byte string
print(type(l)) # byte string

o = open('output.txt', 'w') # write with Text IO
o.write(l.decode('utf-8')) # convert byte string to unicode

o.close()
f.close();

read byte string, output byte string

#!/usr/bin/python

# read string from a file and print it to screen
f = open('temp.txt', 'rb');

l = next(f); # 陈, read a line and save it to byte string
print(type(l)) # byte string

o = open('output.txt', 'wb') # write with Byte IO
o.write(l)

o.close()
f.close();