"Python CookBook2" chapter I text-control case && Access substring

Control Case

Task:

Turns a string from uppercase to lowercase, or to a row.

Solution:

>>> A ='a'. Upper ()>>>a'A'>>> B ='b'. Lower ()>>>b'b'>>>Print "I Love PythOn". Capitalize () I love Python>>>Print "I Love PythOn". Title () I Love Python

Accessing substrings

Task:

Gets a portion of a string.

Solution:

Slicing is a good way, but it can only get one field at a time:

Afield = Theline[3:6]

If you also need to consider the length of the field, Struct.unpack may be more appropriate. For example:

>>>Importstruct>>> Baseformat ="5s 3x 8s 8s">>> Theline ='qqqwwweeerrrtttyyyaaasssdddfff'>>> numremain = Len (theline)-struct.calcsize (Baseformat)>>> format ="%s%ds"%(Baseformat,numremain)>>>Len (theline)30>>> l,s1,s2,t =Struct.unpack (format,theline)>>>L'QQQWW'>>>S1'Errrttty'>>>S2'yyaaasss'>>>T'dddfff'

Note:

Struct.calcsize is used to calculate the length of the result of a format string, such as: Struct.calcsize (' II '), which returns 8

Standard

Format	C Type	Python Type	size	Notes
X	Pad byte	No value
C	Char	string of length 1	1
B	Signed Char	Integer	1	(3)
B	Unsignedchar	Integer	1	(3)
?	_bool	bool	1	(1)
H	Short	Integer	2	(3)
H	Unsignedshort	Integer	2	(3)
I	Int	Integer	4	(3)
I	Unsignedint	Integer	4	(3)
L	Long	Integer	4	(3)
L	Unsignedlong	Integer	4	(3)
Q	Long Long	Integer	8	(2), (3)
Q	Unsignedlong Long	Integer	8	(2), (3)
F	Float	Float	4	(4)
D	Double	Float	8	(4)
S	Char[]	String
P	Char[]	String
P	void *	Integer		(5), (3)

Struct.pack is used to convert the value of Python to a string based on a format character (because there is no byte type in Python, you can interpret the string here as a stream of bytes, or a byte array)

Struct.unpack does work just as opposed to struct.pack, which is used to convert byte streams into Python data types. The function prototype is: Struct.unpack (FMT, String), which returns a tuple.

"Python CookBook2" chapter I text-control case && Access substring