Develop Reference

Regex - Regular expression for counting no.of digits between alphabets

Need to construct a regular expression that counts numbers between alphabets.
schowalte3rguss77ie85 - 2
xyz1zyx - 1
x1y1z1 - 2
I have constructed this . But this doesn't work for case 3.
[[a-z]+[0-9]+[a-z]]*
Any help would be appreciated. Thanks in advance.

Use regx:
(?<=[a-z])\d+(?=[a-z])
Demo: https://regex101.com/r/tpss6x/1
[Javascript]

If you want a count only, the last part should be a lookahead assertion.
If you want to also match uppercase chars, you can make the pattern case insensitive.
[a-z]\d+(?=[a-z])
Explanation
[a-z] Match a single char a-z
\d+ Match 1+ digits
(?=[a-z]) Positive lookahead, assert a char a-z to the right
Regex demo

You can use
(?<=[^\W\d_])\d+(?=[^\W\d_])
See the regex demo. If you want to only support ASCII letters, replace [^\W\d_] (that matches any Unicode letter) with [a-zA-Z].
Details:
(?<=[^\W\d_]) - immediately before the current location, there must be any Unicode letter
\d+ - one or more digits
(?=[^\W\d_]) - immediately after the current location, there must be any Unicode letter.
Counting can be done with len(...), see this Python demo:
import re
text = "schowalte3rguss77ie85"
matches = re.findall(r'(?<=[^\W\d_])\d+(?=[^\W\d_])', text)
print(len(matches)) # => 2

regex: don't match number preceded by certain character

Following code extracts the first sequence of numbers that appear in a string:
num = re.findall(r'^\D*(\d+)', string)
I'd like to add that the regular expression doesn't match numbers preceded by vor V.
Example:
string = 'foobarv2_34 423_wd"
Output: '34'

If you need to get the first match, you need to use re.search, not re.findall.
In this case, you can use a simpler regular expression like (?<!v)\d+ with re.I:
import re
m = re.search(r'(?<!v)\d+', 'foobarv2_34 423_wd', re.I)
if m:
print(m.group()) # => 34
See the Python demo.
Details
(?<!v) - a negative lookbehind that fails the match if there is a v (or V since re.I is used) immediately to the left of the current location
\d+ - one or more digits.
If you cannot use re.search for some reason, you can use
^.*?(?<!v)(\d+)
See this regex demo. Note that \D* (zero or more non-digits) is replaced with .*? that matches zero or more chars other than line break chars as few as possible (with re.S or re.DOTALL, it will also match line breaks) since there is a need to match all digits not preceded with v.
More details:
^ - start of string
.*? - zero or more chars other than line break chars as few as possible
(?<!v) - a negative lookbehind that fails the match if there is a v (or V since re.I is used) immediately to the left of the current location
(\d+) - Group 1: one or more digtis.

Regex to pull the first and last letter of a string

I am using this \d{2}-\d{2}-\d{4} to validate my string. It works to pull the sequence of numbers out of said string resulting in 02-01-1716 however, i also need to pull the letter the string begins with and ends with; i.e. Q:\Region01s\FY 02\02-01-1716A.pdf i need the Q as well as the A so in the end i would have Q: 02-01-1716A

You can use
import re
regex = r"^([a-zA-Z]:)\\(?:.*\\)?(\d{2}-\d{2}-\d{4}[a-zA-Z]?)"
text = r"Q:\Region01s\FY 02\02-01-1716A.pdf"
match = re.search(regex, text)
if match:
print(f"{match.group(1)} {match.group(2)}")
# => Q: 02-01-1716A
See the Python demo. Also, see the regex demo. Details:
^ - start of string
([a-zA-Z]:) - Group 1: a letter and :
\\ - a backslash
(?:.*\\)? - an optional sequence of any chars other than line break chars as many as possible, followed with a backslash
(\d{2}-\d{2}-\d{4}[a-zA-Z]?) - Group 2: two digits, -, two digits, -, four digits, an optional letter.
The output - if there is a match - is a concatenation of Group 1, space and Group 2 values.

You can try:
(.).*(.)\.[^\.]+$
Or with the validation:
(.).*\d{2}-\d{2}-\d{4}(.)\.[^\.]+$

Searching for a pattern in a sentence with regex in python

I want to capture the digits that follow a certain phrase and also the start and end index of the number of interest.
Here is an example:
text = The special code is 034567 in this particular case and not 98675
In this example, I am interested in capturing the number 034657 which comes after the phrase special code and also the start and end index of the the number 034657.
My code is:
p = re.compile('special code \s\w.\s (\d+)')
re.search(p, text)
But this does not match anything. Could you explain why and how I should correct it?

Your expression matches a space and any whitespace with \s pattern, then \w. matches any word char and any character other than a line break char, and then again \s requires two whitespaces, any whitespace and a space.
You may simply match any 1+ whitespaces using \s+ between words, and to match any chunk of non-whitespaces, instead of \w., you may use \S+.
Use
import re
text = 'The special code is 034567 in this particular case and not 98675'
p = re.compile(r'special code\s+\S+\s+(\d+)')
m = p.search(text)
if m:
print(m.group(1)) # 034567
print(m.span(1)) # (20, 26)
See the Python demo and the regex demo.

Use re.findall with a capture group:
text = "The special code is 034567 in this particular case and not 98675"
matches = re.findall(r'\bspecial code (?:\S+\s+)?(\d+)', text)
print(matches)
This prints:
['034567']

Regex include only one digit between chars

I have to parse a PDF document and I'm using PyPDF2 with re(regex).
The file includes several lines like the one below:
18-02-202010:44:48PEDMILANO OVEST- BINASCOA1,40
I need to extract from this line the text( bold ) between the time and the amount:
PEDMILANO OVEST- BINASCOA
The following code is working but sometimes this code doesn't find anything since can be a number between these chars, for example, 18-02-202010:44:48PEDMILANO OVE3ST- BINASCOA1,40.
regex = re.compile(r'\d\d-\d\d-\d\d\d\d\d\d:\d\d:\d\d\D+\d+,\d\d')
Is there a way to include a number in this regular expression?

The following should simplify the current regex:
import re
s = '18-02-202010:44:48PEDMILANO OVE3ST- BINASCOA1,40'
re.search(r'\:\d+([A-Z].*?)(?=\d+\,\d+$)', s).group(1)
# 'PEDMILANO OVE3ST- BINASCOA'
See demo
\d+([A-Z].*?)(?=\d+\,\d+$)
\: matches the character : literally (case sensitive)
\d+: matches a digit (equal to [0-9])
+ Quantifier — Matches between one and unlimited times, as many times as possible, giving back as needed (greedy)
1st Capturing Group ([A-Z].*?)
Match a single character present in the list below [A-Z]
A-Z a single character in the range between A (index 65) and Z (index 90) (case sensitive)
.*? matches any character (except for line terminators)
*? Quantifier — Matches between zero and unlimited times, as few times as possible, expanding as needed (lazy)
Positive Lookahead (?=\d+\,\d+$)
Assert that the Regex below matches
\d+ matches a digit (equal to [0-9])
+ Quantifier — Matches between one and unlimited times, as many times as possible, giving back as needed (greedy)
\, matches the character , literally (case sensitive)
\d+ matches a digit (equal to [0-9])
+ Quantifier — Matches between one and unlimited times, as many times as possible, giving back as needed (greedy)
$ asserts position at the end of a line

I suggest using
import re
text = "18-02-202010:44:48PEDMILANO OVEST- BINASCOA1,40"
print( re.sub(r'^\d{2}-\d{2}-\d{5,6}:\d{2}:\d{2}(.*?)\d+(?:,\d+)?$', r'\1', text) )
It can also be written as
re.sub(r'^\d{2}-\d{2}-\d{5,6}:\d{2}:\d{2}|\d+(?:,\d+)?$', '', text)
Or, if you prefer matching and capturing:
m = re.search(r'^\d{2}-\d{2}-\d{5,6}:\d{2}:\d{2}(.*?)\d+(?:,\d+)?$', text)
if m:
print( m.group(1) )
See an online Python demo. With this solution, your data may start with any char, and will contain any char (excluding line break chars, since your data is on single lines).
Regex details
^ - start of string
\d{2}-\d{2}-\d{5,6}:\d{2}:\d{2} - datetime string: two digits, -, two digits, -, five or six digits, :, two digits, : two digits
(.*?) - Group 1: any zero or more chars other than line break chars, as few as possible
\d+(?:,\d+)? - an int/float value pattern: 1+ digits followed with an optional sequence of , and 1+ digits
$ - end of string.
See the regex demo.