Python String Fundamentals Ch 7

Front 1

3 types of strings in Python

Back 1

str: unicode and ASCII

bytes: for binary data, including encoded text

bytearray: mutable variant of bytes

Front 2

Does python have a type for characters?

Back 2

No. they're just a one-character string

Front 3

create an empty string

Back 3

S = ''

Front 4

Do escape sequences work in Python?

Back 4

yes

Front 5

repeat a string 2x

Back 5

str * 2

Front 6

create a raw string

Back 6

ignores escape sequences

S = r'\temp\spam\'

Front 7

create a byte string

Back 7

B = b'sp\xcm\'

Front 8

create a unicode string

Back 8

U = u'sp\u004c'

Front 9

index a string

Back 9

S[i]

Front 10

slice a string

Back 10

S[:]

Front 11

get the length of a string

Back 11

len(str)

Front 12

search a string

Back 12

myS.find('str')

Front 13

remove whitespace from a string

Back 13

myS.rstrip()

Front 14

replace characters in a string

Back 14

myS.replace('pa', 'xx')

Front 15

split a string on a delimiter

Back 15

myS.split(',')

Front 16

check if a string contains only digits

Back 16

myS.isdigit()

Front 17

convert a string to lowercase

Back 17

myS.lower()

Front 18

check if a string ends with a specified set of characters

Back 18

myS.endswith('spam')

Front 19

delimiter join

Back 19

'Spam'.join(strlist)

#strlist is the list created when you split on delimiters

Front 20

print each character in str

Back 20

for x in str: print(x)

Front 21

check if 'spam' is in a string

Back 21

'spam' in str

Front 22

Why are ' and " interchangeable in Python?

Back 22

so you can embed one of them inside the other without needing an escape sequence

'she said, "yes"'

Front 23

What does Python automatically do to adjacent string literals? How do you prevent his?

'knight' 'knight'

Back 23

concatenates into a single string

use a comma to separate

'knight', 'knight'

Front 24

In Python, is there a null character at the end of a string?

Back 24

no

Front 25

Can Python also use / for directory addresses?

Back 25

yes because it tries to interpret them portably, so you're not just restricted to \

Front 26

create a multiline block string

Back 26

"""

line 1

line 2

"""

#embeds newline characters so it will look like what you typed when it's printed

Front 27

Normally any comments added to the right of a multiline string are included in it. How can you force python to ignore the comments to the right of a multiline string? What's the downside?

Back 27

instead of """, use ( ) around the whole thing

downside: need to use ' ' around each individual part and newline is not included automatically

menu = (

'spam', #comment

'\neggs' # comment)

Front 28

When are triple-quoted strings also used as documentation strings/multiline comments?

Back 28

when they appear at specific points in the file (TBD)

Front 29

Is this a valid expression in Python?

'str'+9

Back 29

no, Python doesn't automatically convert numbers to strings when concatenating

Front 30

difference between .find() and in

Back 30

in returns boolean

find() returns int position of substring

Front 31

slicing: get the second-to-last character in a string

Back 31

S[-2]

Front 32

get all characters after the first letter from a string

Back 32

S[1:]

Front 33

get charaters 1-3 of 'spam'

Back 33

'spam'[1:4]

Front 34

slicing: if omitted, what does the left bound default to? right bound?

Back 34

left bound defaults to 0

right bound defaults to length

Front 35

copy 'spam'

Back 35

s = 'spam'[:]

Front 36

optional third index when slicing

Back 36

stride or step: can use to skip items or reverse order

Front 37

What does this code do?

'ahfdsarea'[1:5:2]

Back 37

from characters 1 up to 5, it gets every 2nd letter

Front 38

collect 'hello' in opposite order

Back 38

S = 'hello'[::-1]

Front 39

Compare this code:

'spam'[1:3]

'spam'[slice(1,3)]

Back 39

equivalent

Front 40

convert "42" to a number

convert 42 to a string

Back 40

int("42")

str(42)

Front 41

change this code so it's valid:

'42' + 1

Back 41

'42' + str(1)

Front 42

difference between str(42) and repr(42)

Back 42

both create a string, but with repr(42) you can recreate the original object, which you can't do with str(42)

Front 43

convert to a floating-point number: '1.234'

Back 43

float('1.234')

Front 44

convert a single character to its ADCII code value, then perform the inverse operation

Back 44

ord('s')

chr(115)

Front 45

In Python, _____ and ____________ generally work across many types, but _______________ are type-specific

Back 45

expressions and built-in functions work across many types, but methods are type-specific

Front 46

How do you get a list of all the names of methods for strings? List with names AND descriptions of all methods?

Back 46

dir(str): names only

help(str): names AND descriptions of methods

help(str.capitalize): look up this method only

Front 47

How can you make in-place changes to a string?

Back 47

use a bytearray: it's mutable

most of the time it's simpler to just use str and replace() though, which creates a new string object

Front 48

If you have a very large string object that needs multiple changes, what can you do?

Back 48

probably too large for a bytearray, so convert to a list with list(s) and then perform operations on list components since it's mutable. Once you're done, use S = ''.join(myList) to join the characters back into a string

#in this case, there's no delimiter so the delimiter at the beginning is empty

Front 49

chop up a string based on delimiters

Back 49

line = 'aaa bbb cccc'

list = line.split()

#since split is empty, it will split on whitespace. otherwise. it will split based on the character or string you pass to it

Front 50

Today, should you use string methods or the string module?

Back 50

string methods only. the string module is ONLY maintained for backwards compatibility and should not be used in new code

Front 51

string formatting expression vs string formatting method call

Back 51

expression: '...%s....' % (values)

'that is %d dead %s' % (1, 'bird')

method call (newer): '...{}...'.format(values)

Front 52

dictionary-based formatting expression example: template with substitution targets

Back 52

'%(qty)d more %(food)s' % {'qty' : 1, 'food' : 'spam'}

# 1 more spam

Front 53

Formatting method: How is it choosing what to format?

template = '{0}, {1}, and {2}'

template.format('spam', 'ham', 'eggs')

Back 53

formatting by position

spam, ham, and eggs

Front 54

Formatting method: How is it choosing what to format?

template = '{motto}, {pork}, and {food}'

template.format(motto='spam', pork='ham', food='eggs')

Back 54

formatting by keyword

spam, ham, and eggs

Front 55

Formatting method: How is it choosing what to format?

template = '{motto}, {0}, and {food}'

template.format('ham', motto='spam', food='eggs')

Back 55

formatting by keyword AND position

spam, ham, and eggs

Front 56

Formatting method: How is it choosing what to format?

template = '{}, {}, and {}'

template.format('spam', 'ham', 'eggs')

Back 56

by relative position

spam, ham, and eggs

Front 57

Which should you use, formatting expression or format method?

Back 57

both are still used and are very similar