# Python – First K consecutive digits in String

Given a String and number K, extract first K consecutive digits making number.

Input : test_str = “geeks5geeks43best”, K = 2
Output : 43
Explanation : 43 is first 2 consecutive digits.

Input : test_str = “geeks5gee2ks439best”, K = 3
Output : 439
Explanation : 439 is first 3 consecutive digits.

Method #1 : Using loop

This is brute way in which this task can be performed. In this, we run a loop through the list and check if valid N consecutive elements are present for current digit, if yes, we return those N elements.

## Python3

 `# Python3 code to demonstrate working of  ` `# First K consecutive digits in String ` `# Using loop ` ` `  `# initializing string ` `test_str ``=` `"geeks5geeks43isbest"` ` `  `# printing original string ` `print``(``"The original string is : "` `+` `str``(test_str)) ` ` `  `# initializing K  ` `K ``=` `2` ` `  `# using loop to run through characters  ` `res ``=` `"" ` `for` `idx ``in` `range``(``len``(test_str) ``-` `K ``+` `1``): ` `        ``is_num ``=` `True` `         `  `        ``# check for valid number of consecutives ` `        ``for` `j ``in` `range``(K): ` `            ``is_num ``=` `is_num & test_str[idx ``+` `j].isdigit() ` `             `  `        ``# extracting numbers  ` `        ``if` `is_num : ` `            ``res ``=` `"" ` `            ``for` `j ``in` `range``(K): ` `                ``res ``+``=` `test_str[idx ``+` `j] ` ` `  `# printing result  ` `print``(``"Required character digits : "` `+` `str``(res))  `

Output

```The original string is : geeks5geeks43isbest
Required character digits : 43
```

Method #2 : Using regex()

This is yet another way in which this task can be performed. In this, we apply valid regex expression and after processing, the result is returned as occurrences, the first one is returned.

## Python3

 `# Python3 code to demonstrate working of  ` `# First K consecutive digits in String ` `# Using regex() ` `import` `re ` ` `  `# initializing string ` `test_str ``=` `"geeks5geeks43isbest"` ` `  `# printing original string ` `print``(``"The original string is : "` `+` `str``(test_str)) ` ` `  `# initializing K  ` `K ``=` `2` ` `  `# using regex() to solve problem ` `temp ``=` `re.search(``'\d{% s}'``%` `K, test_str) ` `res ``=` `(temp.group(``0``) ``if` `temp ``else` `'') ` ` `  `# printing result  ` `print``(``"Required character digits : "` `+` `str``(res))  `

Output

```The original string is : geeks5geeks43isbest
Required character digits : 43
```

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