The task of finding the maximum string length of a specific key in a list of dictionaries involves identifying the longest string associated with the given key. Given a list of dictionaries, the goal is to extract the string values of the specified key, compute their lengths and determine the maximum length. For example, if a = [{'Gfg': "abcd"}, {'Gfg': "qwertyui"}, {'Gfg': "xcvz"}], the maximum length would be 8, corresponding to "qwertyui".

Using Generator Expression

Generator expression efficiently finds the maximum string value length of a key in a list of dictionaries by processing values one at a time, avoiding intermediate storage. Combined with max(), it ensures optimal performance while handling missing or non-string values.

a = [{'Gfg': "abcd", 'best': 2}, 
     {'Gfg': "qwertyui", 'best': 2},
     {'Gfg': "xcvz", 'good': 3},
     {'Gfg': None, 'good': 4}]

f_key = 'Gfg'

res = max((len(sub[f_key]) for sub in a if isinstance(sub.get(f_key), str)), default=0)
print(res)

8

Explanation: generator expression iterates through each dictionary in a, checks if the value of 'Gfg' is a string using isinstance(sub.get(filt_key), str) and computes its length with len(sub[filt_key]) and then max() finds the longest string length, with default=0 ensuring a result of 0 if no valid strings exist.

Using List Comprehension

List comprehension is a concise way to generate a list of values before applying a function like max(). Unlike a generator, it constructs a temporary list in memory before computing the maximum, which can be costly for large datasets.

a = [{'Gfg': "abcd", 'best': 2}, 
     {'Gfg': "qwertyui", 'best': 2},
     {'Gfg': "xcvz", 'good': 3},
     {'Gfg': None, 'good': 4}]

f_key = 'Gfg'

res = max([len(sub[f_key]) for sub in a if isinstance(sub.get(f_key), str)], default=0)
print(res)

8

Explanation: list comprehension filters dictionaries where 'Gfg' is a string, computes its length and stores the results. max() then finds the longest length, with default=0 ensuring a result of 0 if no valid strings exist.

Using map

This functional programming approach applies len() using map() and optionally removes non-string values with filter(). It provides a clean and concise way to process sequences.

a = [{'Gfg': "abcd", 'best': 2}, 
     {'Gfg': "qwertyui", 'best': 2},
     {'Gfg': "xcvz", 'good': 3},
     {'Gfg': None, 'good': 4}]

filt_key = 'Gfg'

res = max(map(len, filter(lambda x: isinstance(x, str), (sub.get(filt_key) for sub in a))), default=0)
print(res)

8

Explanation: generator extracts 'Gfg' values, filter() keeps only strings, map(len, ...) computes their lengths and max() finds the longest, with default=0 ensuring a fallback if no valid strings exist.

Using loop

A traditional for loop iterates through the list, checking each value and updating the maximum string length manually. This method is straightforward and offers explicit control over the logic.

a = [{'Gfg': "abcd", 'best': 2}, 
     {'Gfg': "qwertyui", 'best': 2},
     {'Gfg': "xcvz", 'good': 3},
     {'Gfg': None, 'good': 4}]

filt_key = 'Gfg'

max_length = 0
for sub in a:
    value = sub.get(filt_key)
    if isinstance(value, str):
        max_length = max(max_length, len(value))

print(max_length)

8

Explanation: for loop iterates through each dictionary in a, retrieving the value of 'Gfg' using sub.get(filt_key). If the value is a string, its length is compared with max_length, updating it if the current string is longer.