match ip address
Refer to http://blog.chinaunix.net/uid-108431-id-3350731.html
http://blog.csdn.net/liangyuannao/article/details/8755325
The first step: address analysis, regular initial judgment
- 1, 0-9 \d to match
- 2. 10-99 [1-9]\d to match
- 2. 100-199 1\d\d to match
- 3. 200-249 2[0-4]\d to match
- 4. 250-255 25[0-5] for matching
- Basic expressions can be combined as: \d|[1-9]\d|1\d\d|2[0-4]\d|25[0-5]
- The first three parts of the regular expression are combined into: ((\d|[1-9]\d|1\d\d|2[0-4]\d|25[0-5])\.){3}
- The first three parts plus the last part are combined into: ((\d|[1-9]\d|1\d\d|2[0-4]\d|25[0-5])\.){3 }(\d|[1-9]\d|1\d\d|2[0-4]\d|25[0-5])
Step 3: Further Merge
Can be further combined as:
r = r'((([1-9]?|1\d)\d|2([0-4]\d|5[0-5]))\.){3}(([1-9]?|1\d)\d|2([0-4]\d|5[0-5]))'
After testing, it is found that the ip address with other string filtering will have problems
changed to
r='((?:(?:(?:[1-9]?|1\d)\d|2(?:[0-4]\d|5[0-5]))\.){3}(?:[2-9]|(?:[1-9]|1\d)\d|2(?:[0-4]\d|5[0-4])))\D'
re.findall(r,s)
Notice:
- This regular expression has two flaws:
- 0.0.0.0 cannot be judged
- 255.255.255.255 cannot be judged correctly
- This problem needs to be solved with additional code
built-in functions,
abs() takes absolute value max() min()
divmod(x,y) returns the modulo quotient and remainder callable (function) to determine whether the function can be called
isinstance (x, y) judgment type
str.capitalize() capitalize the first letter of the string
str.replace() String replacement This is a specific replacement, see sub() for fuzzy replacement
string.replace(s, old, new) needs to import the string module
The filter(function, sequence) function acts on the sequence and can be used for sequence filtering
regular expression
r1 = r"\d{3,4}-?"
Compile regular expression as object
re_tel=re.compile(r1)
In this way, the method of re can be called as an object
re_tel.findall('string') returns a list
Matching is case insensitive
re_tel=re.compile(r1,re.I)re.I The attribute of calling re means case insensitive
Whether the object matched by match() is at the beginning of the string, an object is returned. Generally, the return value can be given to a variable to see if the variable is none.
search() matches the string no matter where it is, and it also returns an object
finditer() returns an object iterator after matching, which can be viewed through the next() method. The return is also an object. If you want to see its value, you can use the method group()
A method similar to group() also has
start() returns the position where the match started
end returns the position where the match ends
span returns a tuple containing (start, end)
sub is to intercept the string, but supports multiple delimiters
sub(regular, 'replacement object', original string) This is a fuzzy replacement
re.split(regular, string) supports multiple delimiters and supports regular expressions
r1=r"[\+\-\*]"
re.split(r1,s) uses +, _, *, three strings as separators
Attributes that are often used in regular expressions
re.S makes . match all characters including newlines re.findall(r1, string, re.S)
re.I makes the match case-insensitive
re.M Multi-line matching, affects ^ and $, and multi-line matching. If the regular expression is multi-line, this attribute should also be added
The verbose state of re.X being able to use REs means that it is organized more clearly and comprehensibly
Regular expression grouping
email = r "\w{3}@\w+(\.com|\.cn)"
re.match(email,'[email protected]') will return an object if it matches
re.findall (email, [email protected] ) returns the matched group string [.com]
if we have a string s=''' sdf hello sun=westos t43
wefs sun=no t43 sdf
hello sun=ni t43 sddsf'''
r1=r"hello sun=.+ t43"
All matched data returned by re.findall(r1,s) ['hello sun=westos t43','hello sun=ni t43']
If we do group processing
r1=r"hello sun=(.+) t43"
The priority returned by re.findall(r1,s) is the data in the group, that is, the data matching the group ['westos','ni']
match can also match
This can be used by web crawlers to get the url or ip we want to get