String methods

Question 1

Return a copy of the string with its first character capitalized and the rest lowercased.

Answer 1

str.capitalize()

Question 2

What does str.center(width[, fillchar]) ?

Answer 2

Return centered in a string of length width. Padding is done using the specified fillchar (default is a space).

>>> 'text'.center(10)
>>> 'text'.center(10, '#')
'###text###'
>>> 'text'.center(11, '#')
'####text###'

Question 3

How to count char / substring in str?

Answer 3

str.count(sub[, start[, end]])

Return the number of non-overlapping occurrences of substring sub in the range [start, end]. Optional arguments start and end are interpreted as in slice notation.

Question 4

How to decode / encode?

Answer 4

str. decode([encoding[, errors]])
str. encode([encoding[, errors]])

Encodings: ‘utf-8’, ‘ascii’

Question 5

Check if str ends with given suffix.

Answer 5

str.endswith(suffix[, start[, end]]) # returns True or False

Question 6

How to replace \t tabs with given indend size?

Answer 6

> > > ‘01\t012\t0123\t01234’.expandtabs() # default is 8
‘01 012 0123 01234’
‘01\t012\t0123\t01234’.expandtabs(4)
‘01 012 0123 01234’

Question 7

Find substring in the given str.

Answer 7

str.find(sub[, start[, end]])

Returns an index of the first substring occurrence. -1 if not found.

To check if sub is a substring or not, don’t use .find, use the in operator:

> > > ‘Py’ in ‘Python’
True

Question 8

What’s the diff between str.index and str.find methods?

Answer 8

They’re almost the same, but index also raises ValueError when the substring is not found. Find returns -1 if nothing found.

Question 9

How to format strings with .format?

Answer 9

Args are called by indices. Your kwargs can be **any_dict or keyworded args, they can be called by the keys.

> > > ‘{0} {1} {a}’.format(‘o’, ‘one1’, **{‘a’: ‘a char’})
‘o one1 a char’

> > > ‘{0} {1} {a}’.format(‘o’, ‘one1’, a=’a char’)
‘o one1 a char’

for format tricks see separate deck for it!

Question 10

How to check if there is at least one character and all chars are alphabetic?

Answer 10

str.isalpha() # True / False

Question 11

How to check if there is at least one character and all chars are digits?

Answer 11

str.isdigit() # True / False

Question 12

How to check if there is at least one character and all chars are lowercase?

Answer 12

str.islower() # True / False

Question 13

How to check if there is at least one character and all chars are whitespaces?

Answer 13

str.isspace()

Question 14

How to check if there is at least one character and the string is title-cased (first letter in every word is upper-case, all next - lower-case)?

Answer 14

str.istitle()

Question 15

How to check if there is at least one character and all chars are uppercase?

Answer 15

str.isupper()

Question 16

Concatenate / build the string from the iterable.

Answer 16

separator_str.join(iterable)

> > > l = [‘1’,’2’,’3’]
‘, ‘.join(l)
‘1, 2, 3’

Question 17

How to get left-justified string?

Answer 17

str.ljust(width[, fillchar])
Padding is done using the specified fillchar (default is a space). The original string is returned if width is less than or equal to len(s)

> > > info = {‘name’:’nick’, ‘surname’:’bulow’, ‘age’:’153’}
for k, v in info.items(): print k.ljust(10), v
“age 153
surname bulow
name nick”

brainscape font is not fixed width, so output example is broken. second column should have straight order.

Question 18

How to get right-justified string?

Answer 18

str.rjust(width[, fillchar])

Question 19

How to convert all str chars to lowercase?

Answer 19

str.lower()

Question 20

How to strip given leading and trailing characters from the string?

Answer 20

str.strip([chars])

> > > ’ spacious ‘.strip()
‘spacious’
‘www.example.com’.strip(‘cmowz.’)
‘example’

Question 21

How to strip given leading (left side) characters from the string?

Answer 21

str.lstrip([chars])

> > > ’ spacious ‘.lstrip()
‘spacious ‘
‘www.example.com’.lstrip(‘cmowz.’)
‘example.com’

Question 22

How to strip given trailing (right side) characters from the string?

Answer 22

str.rstrip([chars])

> > > ’ spacious ‘.rstrip()
‘ spacious’
‘mississippi’.rstrip(‘ipz’)
‘mississ’

Question 23

What is the purpose of str.partition(sep) ?

Answer 23

Split the string at the first occurrence of sep, and return a 3-tuple containing the part before the separator, the separator itself, and the part after the separator. If the separator is not found, return a 3-tuple containing the string itself, followed by two empty strings.

> > > ‘super-hero’.partition(‘-‘)
(‘super’, ‘-‘, ‘hero’)
‘superhero’.partition(‘-‘)
(‘superhero’, ‘’, ‘’)

Question 24

How to replace chars / substring in the str?

Answer 24

str.replace(old, new[, count])

Return a copy of the string with all occurrences of substring old replaced by new. If the optional argument count is given, only the first count occurrences are replaced.

Question 25

How to find the first occurence of substr starting from the right side in the reverse order?

Answer 25

str.rfind(sub[, start[, end]])

Question 26

What’s the diff between str.rindex and str.rfind methods?

Answer 26

They’re almost the same, but rindex also raises ValueError when the substring is not found. Rfind returns -1 if nothing found.

Question 27

What is the purpose of str.rpartition(sep) ?

Answer 27

Split the string at the last occurrence of sep, and return a 3-tuple containing the part before the separator, the separator itself, and the part after the separator. If the separator is not found, return a 3-tuple containing two empty strings, followed by the string itself.

Question 28

How to check if there is at least one character and all chars are alphabetic and / or numeric?

Answer 28

str.isalnum()

Question 29

How to split lines by the given separator?

Answer 29

str.split([sep[, maxsplit]])

Question 30

What if two or more separators stand alongside each other in the string to be split?
like ‘1,,2’.split(‘,’)

Answer 30

> > > ‘1,,2’.split(‘,’)
[‘1’, ‘’, ‘2’]
‘1,,,2’.split(‘,’)
[‘1’, ‘’, ‘’, ‘2’]

Question 31

Can split separator contain more than one char?

Answer 31

Sure! ‘1<>2<>3’.split(‘<>’) returns [‘1’, ‘2’, ‘3’]

Question 32

What if you split empty str?

Answer 32

You get list with empty str obj in it
»> ‘‘.split(‘.’)
[’’]

Question 33

What if no split separator is provided or it is None?

Answer 33

A different splitting algorithm is applied: runs of consecutive whitespace are regarded as a single separator, and the result will contain no empty strings at the start or end if the string has leading or trailing whitespace. Consequently, splitting an empty string or a string consisting of just whitespace with a None separator returns [].
>>> ' 1  2   3  '.split()
['1', '2', '3']
>>> '  1  2   3  '.split(None, 1)
['1', '2   3  '].

Question 34

How to start splitting text moving in right to left order?

Answer 34

str.rsplit([sep[, maxsplit]])
# main idea of rsplit is to be used with maxsplit, without it is just split.

Question 35

What is the purpose of str.splitlines

Answer 35

str.splitlines([keepends])
Return a list of the lines in the string, breaking at line boundaries (“\r”, “\n”, and “\r\n” are line boundaries).

If keepends is True - save line boundaries char in the output.

> > > ‘ab c\n\nde fg\rkl\r\n’.splitlines()
[‘ab c’, ‘’, ‘de fg’, ‘kl’]
‘ab c\n\nde fg\rkl\r\n’.splitlines(True)
[‘ab c\n’, ‘\n’, ‘de fg\r’, ‘kl\r\n’]

Question 36

Describe diff between split and splitlines.

Answer 36

Unlike split() when a delimiter string sep is given, this method returns an empty list for the empty string, and a terminal line break does not result in an extra line:

> > > ”“.splitlines()
[]
“One line\n”.splitlines()
[‘One line’]

For comparison, split(‘\n’) gives:
»>

> > > ’‘.split(‘\n’)
[’’]
‘Two lines\n’.split(‘\n’)
[‘Two lines’, ‘’]

Question 37

unicode splitlines

Answer 37

unicode splitlines

Question 38

Check if str starts with given suffix.

Answer 38

str.startswith(suffix[, start[, end]]) # returns True or False

Question 39

How to swap case?

Answer 39

str.swapcase()

Question 40

Return a titlecased version of the string.

Answer 40

str.title()
»> “they’re bill’s friends from the UK”.title()
“They’Re Bill’S Friends From The Uk”

Question 41

How to avoid text after apostrophies to be titlecased?

Answer 41

> > > import re
def titlecase(s):
… return re.sub(r”[A-Za-z]+(‘[A-Za-z]+)?”,
… lambda mo: mo.group(0)[0].upper() +
… mo.group(0)[1:].lower(),
… s)
…
titlecase(“they’re bill’s friends.”)

Question 42

What is unicode.splitlines() ?

Answer 42

Return a list of the lines in the string, like str.splitlines(). However, the Unicode method splits on the following line boundaries:

Representation 	Description
\n 	Line Feed
\r 	Carriage Return
\r\n 	Carriage Return + Line Feed
\v or \x0b 	Line Tabulation
\f or \x0c 	Form Feed
\x1c 	File Separator
\x1d 	Group Separator
\x1e 	Record Separator
\x85 	Next Line (C1 Control Code)
\u2028 	Line Separator
\u2029 	Paragraph Separator

Question 43

How to update existing chars in the string by the chars from given translation table?

Answer 43

Use str.translate(table[, deletechars]). For table creation use helper func from string import maketrans(from, to):

> > > from string import maketrans
table = maketrans(‘aeio’, ‘4310’)
‘hello interesting world’.translate(table)
‘h3ll0 1nt3r3st1ng w0rld’

Question 44

How to convert all str chars to uppercase?

Answer 44

str.upper()

Question 45

What is str.zfill?

Answer 45

str.zfille(width) # return string filled left with len(str) - width zeros:

> > > ‘test’.zfille(7)
‘000test’

Question 46

unicode.isnumeric() unicode.isdecimal()¶

Answer 46

unicode.isnumeric() unicode.isdecimal()¶